I would run an AVG scan and the Ad-Aware scan just in case something has got through. You could try a hijack this log. That would certainly find the root of the problem. I myself don't understand them but i can get someone to come over and have a look over it.
I believe that this is the most up-to-date version to my knowledge:
http://www.majorgeeks.com/download5554.html
Download it run it, post the log here, and i shall get someone to have a look over it for ya.

Logfile of Trend Micro HijackThis v2.0.2
Scan saved at 5:01:09 PM, on 12/16/2007
Platform: Windows Vista (WinNT 6.00.1904)
MSIE: Internet Explorer v7.00 (7.00.6000.16575)
Boot mode: Normal

Running processes:
C:\Windows\system32\Dwm.exe
C:\Windows\system32\taskeng.exe
C:\Windows\Explorer.EXE
C:\Program Files\Windows Defender\MSASCui.exe
C:\hp\support\hpsysdrv.exe
C:\Windows\RtHDVCpl.exe
C:\Program Files\HP\HP Software Update\hpwuSchd2.exe
C:\Windows\system32\schtasks.exe
C:\Windows\System32\rundll32.exe
C:\Program Files\Grisoft\AVG7\avgcc.exe
C:\Program Files\Zune\ZuneLauncher.exe
C:\Program Files\Windows Sidebar\sidebar.exe
C:\Windows\System32\rundll32.exe
C:\Program Files\Hewlett-Packard\HP Advisor\HPAdvisor.exe
C:\Windows\ehome\ehtray.exe
C:\Program Files\Windows Media Player\wmpnscfg.exe
C:\Program Files\Snapfish Picture Mover\SnapfishMediaDetector.exe
C:\Windows\ehome\ehmsas.exe
C:\Windows\system32\wbem\unsecapp.exe
C:\hp\kbd\kbd.exe
C:\Program Files\Internet Explorer\ieuser.exe
C:\Windows\system32\SearchFilterHost.exe
C:\Users\Kyle\Downloads\HiJackThis.exe

R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Page = http://go.microsoft.com/fwlink/?LinkId=54896
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://www.gamefaqs.com/
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://ie.redirect.hp.com/svs/rdr?TY...ion&pf=desktop
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Default_Search_URL = http://go.microsoft.com/fwlink/?LinkId=54896
R1 - HKLM\Software\Microsoft\Internet Explorer\Main,Search Page = http://go.microsoft.com/fwlink/?LinkId=54896
R0 - HKLM\Software\Microsoft\Internet Explorer\Main,Start Page = http://ie.redirect.hp.com/svs/rdr?TY...ion&pf=desktop
R0 - HKLM\Software\Microsoft\Internet Explorer\Search,SearchAssistant =
R0 - HKLM\Software\Microsoft\Internet Explorer\Search,CustomizeSearch =
R0 - HKCU\Software\Microsoft\Internet Explorer\Toolbar,LinksFolderName =
O1 - Hosts: ::1 localhost
O2 - BHO: (no name) - {02478D38-C3F9-4efb-9B51-7695ECA05670} - (no file)
O2 - BHO: Adobe PDF Reader Link Helper - {06849E9F-C8D7-4D59-B87D-784B7D6BE0B3} - C:\Program Files\Common Files\Adobe\Acrobat\ActiveX\AcroIEHelper.dll
O2 - BHO: Spybot-S&D IE Protection - {53707962-6F74-2D53-2644-206D7942484F} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O2 - BHO: SSVHelper Class - {761497BB-D6F0-462C-B6EB-D4DAF1D92D43} - C:\Program Files\Java\jre1.6.0_01\bin\ssv.dll
O4 - HKLM\..\Run: [Windows Defender] %ProgramFiles%\Windows Defender\MSASCui.exe -hide
O4 - HKLM\..\Run: [hpsysdrv] c:\hp\support\hpsysdrv.exe
O4 - HKLM\..\Run: [KBD] C:\HP\KBD\KbdStub.EXE
O4 - HKLM\..\Run: [RtHDVCpl] RtHDVCpl.exe
O4 - HKLM\..\Run: [HP Health Check Scheduler] c:\Program Files\Hewlett-Packard\HP Health Check\HPHC_Scheduler.exe
O4 - HKLM\..\Run: [Adobe Reader Speed Launcher] "C:\Program Files\Adobe\Reader 8.0\Reader\Reader_sl.exe"
O4 - HKLM\..\Run: [SunJavaUpdateReg] "C:\Windows\system32\jureg.exe"
O4 - HKLM\..\Run: [HP Software Update] c:\Program Files\HP\HP Software Update\HPWuSchd2.exe
O4 - HKLM\..\Run: [NvSvc] RUNDLL32.EXE C:\Windows\system32\nvsvc.dll,nvsvcStart
O4 - HKLM\..\Run: [NvCplDaemon] RUNDLL32.EXE C:\Windows\system32\NvCpl.dll,NvStartup
O4 - HKLM\..\Run: [NvMediaCenter] RUNDLL32.EXE C:\Windows\system32\NvMcTray.dll,NvTaskbarInit
O4 - HKLM\..\Run: [AVG7_CC] C:\PROGRA~1\Grisoft\AVG7\avgcc.exe /STARTUP
O4 - HKLM\..\Run: [Zune Launcher] "c:\Program Files\Zune\ZuneLauncher.exe"
O4 - HKLM\..\RunOnce: [Launcher] %WINDIR%\SMINST\launcher.exe
O4 - HKCU\..\Run: [Sidebar] C:\Program Files\Windows Sidebar\sidebar.exe /autoRun
O4 - HKCU\..\Run: [HPADVISOR] C:\Program Files\Hewlett-Packard\HP Advisor\HPAdvisor.exe autoRun
O4 - HKCU\..\Run: [ehTray.exe] C:\Windows\ehome\ehTray.exe
O4 - HKCU\..\Run: [WMPNSCFG] C:\Program Files\Windows Media Player\WMPNSCFG.exe
O4 - HKUS\S-1-5-19\..\Run: [Sidebar] %ProgramFiles%\Windows Sidebar\Sidebar.exe /detectMem (User 'LOCAL SERVICE')
O4 - HKUS\S-1-5-19\..\Run: [WindowsWelcomeCenter] rundll32.exe oobefldr.dll,ShowWelcomeCenter (User 'LOCAL SERVICE')
O4 - HKUS\S-1-5-19\..\Run: [AVG7_Run] C:\PROGRA~1\Grisoft\AVG7\avgw.exe /RUNONCE (User 'LOCAL SERVICE')
O4 - HKUS\S-1-5-20\..\Run: [Sidebar] %ProgramFiles%\Windows Sidebar\Sidebar.exe /detectMem (User 'NETWORK SERVICE')
O4 - HKUS\S-1-5-18\..\Run: [AVG7_Run] C:\PROGRA~1\Grisoft\AVG7\avgw.exe /RUNONCE (User 'SYSTEM')
O4 - HKUS\.DEFAULT\..\Run: [AVG7_Run] C:\PROGRA~1\Grisoft\AVG7\avgw.exe /RUNONCE (User 'Default user')
O4 - Global Startup: Snapfish Media Detector.lnk = C:\Program Files\Snapfish Picture Mover\SnapfishMediaDetector.exe
O9 - Extra button: (no name) - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Program Files\Java\jre1.6.0_01\bin\ssv.dll
O9 - Extra 'Tools' menuitem: Sun Java Console - {08B0E5C0-4FCB-11CF-AAA5-00401C608501} - C:\Program Files\Java\jre1.6.0_01\bin\ssv.dll
O9 - Extra button: (no name) - {DFB852A3-47F8-48C4-A200-58CAB36FD2A2} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O9 - Extra 'Tools' menuitem: Spybot - Search & Destroy Configuration - {DFB852A3-47F8-48C4-A200-58CAB36FD2A2} - C:\PROGRA~1\SPYBOT~1\SDHelper.dll
O13 - Gopher Prefix:
O17 - HKLM\System\CCS\Services\Tcpip\..\{987D9242-0748-41B7-82C3-5D3D62D5B19A}: NameServer = 209.244.0.3 209.244.0.4
O20 - Winlogon Notify: avgwlntf - C:\Windows\SYSTEM32\avgwlntf.dll
O23 - Service: Ad-Aware 2007 Service (aawservice) - Lavasoft AB - C:\Program Files\Lavasoft\Ad-Aware 2007\aawservice.exe
O23 - Service: AVG7 Alert Manager Server (Avg7Alrt) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVG7\avgamsvr.exe
O23 - Service: AVG7 Update Service (Avg7UpdSvc) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVG7\avgupsvc.exe
O23 - Service: AVG7 Resident Shield Service (AvgCoreSvc) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVG7\avgrssvc.exe
O23 - Service: AVG E-mail Scanner (AVGEMS) - GRISOFT, s.r.o. - C:\PROGRA~1\Grisoft\AVG7\avgemc.exe
O23 - Service: HP Health Check Service - Hewlett-Packard - c:\Program Files\Hewlett-Packard\HP Health Check\hphc_service.exe
O23 - Service: InstallDriver Table Manager (IDriverT) - Macrovision Corporation - c:\Program Files\Common Files\InstallShield\Driver\1050\Intel 32\IDriverT.exe
O23 - Service: LightScribeService Direct Disc Labeling Service (LightScribeService) - Hewlett-Packard Company - c:\Program Files\Common Files\LightScribe\LSSrvc.exe
O23 - Service: lxba_device - - C:\Windows\system32\lxbacoms.exe
O23 - Service: RoxMediaDB9 - Sonic Solutions - c:\Program Files\Common Files\Roxio Shared\9.0\SharedCOM\RoxMediaDB9.exe
O23 - Service: SBSD Security Center Service (SBSDWSCService) - Safer Networking Ltd. - C:\Program Files\Spybot - Search & Destroy\SDWinSec.exe
O23 - Service: stllssvr - MicroVision Development, Inc. - c:\Program Files\Common Files\SureThing Shared\stllssvr.exe
O23 - Service: XAudioService - Conexant Systems, Inc. - C:\Windows\system32\DRIVERS\xaudio.exe

--
End of file - 7067 bytes

oh my that is quite alot of programs runnig when you startt he pc, what exactly are you doing when the BSOD happen, browse, games,word processor, do you have windows defender running on the PC? does this PC have a pci video card or onboard? how many stick of memory does it have?

Sometimes the computer is just sitting there and it blue screens. Windows Defender is running I'm pretty sure. It has an onboard card, and it has 3GB of RAM

Sometimes my vista doesn't find the updates for all my drivers and I have to go to the manufacturer's site of the installed items (graphic cards, sound cards, etc). I keep autoupdate on for microsoft also and recommend it. Oh you have x64 bit version of vista, don't you? I'm not familiar with that one. Have you tried running scan disk at bootup? You'll have to set it in windows and when you boot next time it'll run. I'll bet you it's a driver or one of those softwares though.. Maybe you can trouble shoot them by disabling some of them for a bit. (I'd probably get off line to do that for safety reasons).

You sound like a great person, hope this gets going for ya.

xts

I don't think I have the x64 bit version of Vista, I might though. I have run the Windows Update and there are no new updates.

you might be having a conflick with windows defender and avg, uninstall/disable one and see what happen, also i would try and shutdown some of those startup programs, you have way too much starting up with windows, and most not needed.

But would a conflict between the 2 virus programs really be causing the Blue Screen of Death?

yes it can, it is recommended that you dont run both at the same time especially if they are going to start with windows. uninstall one and see what happens

Does Windows Defender still protect against viruses though? I don't wanna be open to them.