Most of the big security software providers will actually give you a full free trial for between 3 and 12 months ( and then they’ll often subsequently do a cheap subscription offer). If you go to the security section in windows it should give you a load of links to free trials, if not just go to McAfee.
yep lavasoft adaware se is free and will get rid of any malware and a few types of data miner stuff but isn’t really a virus thing, spy bot is kind of the same tool and is limited in it’s ability as an antivirus and these programs selectively looks for programs that aren’t specifically malicious viruses.
downloads.com has been known to dish out a certain amount of spyware with some downloads. Mostly just tracking cookies though.
Spybot is very good, I find that it is both simple and efficeint. It does however change/delete the parts of the registry…which I heard isn’t too good a thing to do.