If I may horn in for a moment, two well-recommended free antiviruses, which install on your drive, are:
AVG 7.0 free edition
http://free.grisoft.com/freeweb.php/doc/2/
Free avast! 4 Home Edition
http://www.avast.com/eng/avast_4_home2.html
In addition, it doesn't hurt to run an onlinescan, which sometimes catches things- this one:
HouseCall
http://housecall-beta.trendmicro.com/en/start_corp.asp
has been upgraded to scan for viruses, trojans, spyware, and security holes.
tsd3 is very good.
even ms' beta antispyware is good; mainly it came from giant who got it from counterspy. counter runs on win98, ms' beta does not run on win98