As the guy who often spends more time fixing everyone else's PCs up than he does his own job, I discourage people who aren't 100% confident with what they are doing when it comes to spyware and virus removal.
There are many bogus pieces of software under the guise of spyware/virus removal or system optimisation tools which actually do the opposite - often slow your PC down by installing its own spyware - and as previously mentioned, some poor sods fall for it and give out their bank details in hope of getting it sorted.
A few points I've picked up from doing this - quite a lot of times, for various colleagues, family and friends. Sounds like Defiler's done it a few times too...
I steer well clear of things which strongly advertise themselves as free utilities unless I trust their source. AVG is a reasonable free virus scanner but I have removed viruses from several people's PCs who use it therefore I don't see it as that reliable. I strongly recommend
Eset's NOD32. It is not free but when I bought my license it cost less than Norton and the mainstream competitors, and it performs faster, uses less memory. It has not let me down yet. Playing it on the safe side, don't install any anti virus/spyware if you've not heard of it before or it hasn't been recommended by someone you trust.
Be prepared to potentially spend a LOT of time on it, but awkwardly a lot of that time is spent waiting for different pieces of software to scan your PC. Zzzz. There are times I've spent a couple of days on a machine removing spyware for people. If you have no valuable info or you have backed it up, sometimes it really is easier to format your hard drive and reinstall windows/software, but you won't know unless you try removal and I have never had to resort to that, touch wood.
Use combinations of several tools, no one piece of software will detect all problems, and as BG has now found out, some nasties can even disable your virus shield/firewall/ineternet connection rendering your PC vulnerable or unable to download any fixes. Very irritating...
My top tools for getting rid of the bugs are
Spybot - S&D, Microsoft Antispyware/Windows Defender (yep it is actually worth a shot),
Killbox (used for ending stubborn processes and removing protected files)
HijackThis (a free browser hijack analysis tool),
Process Explorer (useful monitor tool to see what processes and services are running and see their individual memory/processor usage)
Hope this helps, spyware/virus removal really sucks and I hate doing it. Good luck!