Im not a fan of cumbersome antivirus programs due to the fact they are slow
and, cumbersome?. I use NOD 32 from Eset which is fast and detects well but
is not too good at removing viruses. There are other free virus detectors
that don't slow your system down, AVG comes to mind, or you can just do a
scan weekly with some online virus scan utility like: http://security.symantec.com/sscv6/default.asp?langid=ie&venid=sym .limit
your start up programs and you will see an improvement in startup speed.