Adware / spyware / virus protection for Vista

I came across a nice guide to computer safty in this forum, only problem is that that alot of the software is not compatibaly with Vista.

Suggestions?

If I were to change the compatability of the shareware to run with XP will they still work effectively?

I currently run a few programs that way and have no issues, but for security reasons I would like some input on the steps to take.

Right now I have Norton and Windows Defender up and runnning with the installed firewall.