How do I rid my Vista PC of viruses /spy,adware?

It seems that I have alot of trojans,viruses,and assorted security issuess on my vista desktop PC Ive run AVG,Bit defender,widows defender,Norton,spybot,avast,and regesstry cleaner none solve my problem when I scan with spyware/adware remover it claims to have 41 infected files does anyone know a really good free program that will remove all my pc troubels . I bought this regestry cleaner but its not doing anything to help I need this machien fixed before it gets way beyond repair mabey I should reformat it but not sure how to do it myself if anyone knows the best soulution please tell me (I thought of trashing this PC so dont bother saying it it cost me too much to throw out just yet Vista sucksI know)! Thanks

You can free download antispyware 2008
http://www.anti-spyware-2008.com which is an essential tool to keep your system free of dangerous spywares, protecting your privacy and your PC.
It also works very well for me

AVG 8.0 Free Review Part 1