It is often ignored, but Windows (XP and Vista) has a fairly good antivirus.
To get there just click on "start"then"execute" and type the following line (copy / paste)
% Systemroot% / system32/MRT.exeIn the new window click "Next"then choose the method of analysis:if you just want to do a quick analysis you can choose quick analysis.
If it's for a check after infection choose full scan
and if you want to scan a folder, file, USB or CD-ROM select custom scan and define the "object" of your concerns.
To help you optimize and secure your computer
Careful, this virus is not sufficient to work alone because it does not work in the background and does not scan your computer continuously, but only on request.
It should be used to perform regular scans of your PC, for safety (in case a virus or worm is passed through the mesh of your other anti virus) or following an infection found to eradicate files contamination that may remain in your computer