So now you can't access the files at all? When do you get the explorer.exe error? On log-in? If you open a folder?

You can do a Ctrl+Alt+Del and look in the Task Manager, see what else is running that doesn't need to be, and close it (right-click, hit "End Process") and see if that keeps Explorer happy. If it's a needed process it won't let you close it, so don't feel like you're going to break anything here. vs7jit.exe is a good place to start if it is present, and if this works, doing a Start, Run, type

"C:\Program Files\Common Files\Microsoft Shared\VS7Debug" /regserver

and reboot might help permanently. If msiexec.exe is to blame, reinstall Windows Installer and do a similar Start -> Run with C:\winnt\system32\msiexec.exe as the address.

If you can't access the data at all because of Explorer crashing, but have access to another computer and a genuine XP CD, I'd suggest going to http://www.nu2.nu and creating a boot disc to get your data to a USB drive, or find out what NIC driver it takes and add it to the files pebuilder.exe will use to create the disc to allow networking the files to another computer (USB drivers are included, but you have to supply your own NIC drivers). Scroll down to the downloads and "Getting Started" section on the link to start you on your way. After you have your data, I would concur with your IS guy - time to "wipe and reload", reinstall 2000.