Download CWShredder 2.14 from here:
http://www.intermute.com/products/cwshredder.html
Run it, and press the Fix button (not scan). Close all windows before hitting the Fix button.
For every User listed under C:\Documents and Settings, delete the entire contents of these folders (not the folders themselves):
Cookies
History
Local Settings\Temp
Local Settings\Temporary Internet Files\Content.IE5
Delete the entire contents of your C:\Windows\Temp folder.
Delete the entire contents of your C:\Temp folder (if you have one).
Do a search for *.tmp and delete all entries found.
Go to Start, Run, and type in cleanmgr, and then click OK. Select the drive XP is on, and check the boxes for Downloaded Program Files (move any files you wish to keep out of this folder first), Temporary Internet Files, Recycle Bin, Temporary Files, Temporary Offline Files, Offline Files, (and Compress old files & Catalog files for the Content Indexer if you wish), and then click OK. Click Yes to confirm you want these files deleted. It may take awhile for this to run, please be patient.
Note: if any of these temporary files cannot be deleted while in normal mode, try Safe Mode.
Empty your Recycle Bin, reboot, close any open browser windows, scan with hijackthis, and post a new log please.
You can also try an in-place upgrade (aka repair installation); instructions can be found here:
http://support.microsoft.com/default.aspx?scid=kb;en-us;315341&Product=winxp