So, I was trying to set up a development environment to test Visual Studio 2010 RC out and ran across this nugget of assholery - IIS 5.1 (the highest version that comes with XP and cannot be 'upgraded') DOES NOT WORK WITH .NET 4.O. And Visual Studio 2010 won't start unless .NET 4.x is installed. So basically, if you want to try out VS 2010, you're stuck either using the built-in server, or IIS 6+.

Weak.