We use both of these programs with Vista and XP. We highly recommend them.
You can try them at No Cost
Registry Smart  and Repair XP Pro 100% XP & Vista Compatible
(Great programs) The most comprehensive system repair tools on the market.
 

Microsoft has a online safety scanner for your computer at http://safety.live.com
We used it and it's works well however it does some time to complete because it does so much.

* The hottest Registry cleaning software on the Net today!

* Repair XP Pro - (Great program) The most comprehensive system repair tool on the market.

* Scan your PC for errors absolutely Free (Very good)

* If you use Google AdSense™ Read this page Correct Keywords can pay you more money

* Evidence Eliminator - Erase your surfing history total "privacy protection".

* Double the speed of your PC!Discover the secrets to speed up and optimize your PC in minutes!

* 100's of Very Good Assorted Free computer programs.