For me, i'll rather try other method instead of worrying was the software free? was my anti-spyware database up-to-date? can my anti-spyware get rid of trojans or rootkit? annoyed by the slow performance by using all those software~

For instance, i used a tool called 'WormRadar' to suck up all the viriis & malware for me. You also can used 'VMWare' (it's free now for Player) to test on some software or visit to some malicious site(just take a snapshot before & after). You can also try 'Software Virtualization Solution' (free for Personal Use) to inspect application that you install or just roll-back(reset) in a single click.

Further more, some extra configuration might avoid you to all those malicious code/ware, like configure your browser for disallow some source (activeX, javascirpt...), avoid cookies/cache storing, etc.... get yourself a personal firewall, so that each and every inbound & outbound is not beyond your notice. Inspect every outbound connection(might be dial-home or download stuff) and deny it if look unfriendly.

Lastly if you really want a virus/spyware-free OS, try use (Trusted)Live-CD each and everytime you do your stuff (surf net, send mail, test apps, etc...). Once you have done your stuff, reboot, everything goes back as clean as NEW~ (of'cos u need to figure out how to save your file/doc in another media,etc..) Or, alternative optive will be a Hardware-based Reboot card( JustReboot or Innov8) to restore your PC back to normal everytime you reboot.

Hope you will enjoy the world of Virus-free realm~ ^_<