Dell Optiplex 210L

Hello everyone!
I'm helping a friend recover his computer from a virus attack. F8+scans were able to remove most of the viruses except for two. The other two were removed as follows:
1- was located in the folder "c:\system volume information." Live Scanner was able to remove it after shutting down system restore.
2- was located in "c:\documents and settings\local service\ local configuration \....." (don't remember the exact path). The ONLY way i was able to remove this one (it was called UPDATE.EXE and was located inside a UPDATE.CAB and windows live scan reported it to be called "zwangi") was to boot into Ubuntu and manually delete the UPDATE.CAB file.
After scanning the computer was fully clean again.

BUT PLUGnPLAY service made the computer freeze after all desktop items were loaded. Also, windows media player would not play audio files. So I narrowed the problem down to this:
PLUGnPLAY service = ON - the computer freezes WITH the SIGMATEL AUDIO DRIVER FROM DELL
PLUGnPLAY service = OFF - the computer DOES NOT FREEZE EVER
PLUGnPLAY service = ON AND SIGMATEL DRIVER = REMOVED - COMPUTER NEVER FREEZES

Needless to say, the audio NEVER works for any system sounds or WMP.

PLEASE HELP us!!! I've been trying to solve the issue for a couple days now  
I've done HDD diagnostics, CHKDSK, CHKDSK /R and uninstalling/installing audio drivers from Dell website.