First run the hdd manufacturers diagnostic disk on the drive, sounds like it could be a hdd problem.
Then try running chkdsk on the drive in question.
Also have a look in Event Viewer and see what errors are listed.
Performance and Maintenace
Highlight a error then click properties, then click on the link below For more information, see Help and Support Center as
this may give you information on how to solve the error.
Can you uninstall the drivers and just use the WinXP generic ones? Does the PC still run slow?
However if you think that the PC is infected submit a hijackthis log here.How to submit a hijackthis logDownload Hijackthis
Try running the following from safe mode (Getting to safe-mode
you'll also need the virus template file from here
Also try installing and running A2 Free
I'd also run Spybot
If your using Win2K/XP run adaware/spybot from "safe mode with command prompt"
At the C:\ prompt type the following:-
C:\progra~1\spybot~1\spybotsd.exe /autocheck /autofix