I use Windows to build Ruby gems, for a smart-card simulator, and to see my sites in IE.

Therefore I install the following: disable anti-virus warning, disable firewall + warnings, all updates, Firefox, Safari (also gets me Bonjour), One-click Ruby, Eclipse, Aptana Studio, Git (the msys port), Visual Studio 6 SP6.

Caveat: my latest Windows (XP) installs are in a VirtualBox VM.