The problem with .NET framework is some versions also require the installation of the previous version. I can't recall if version 3.0 required that version 2.0 was installed, I don't know if version 3.5 has any prerequisites.
I started out with version 1.0, installed the 1.1 update and then version 2.0, this didn't require that version 1 was installed so I uninstalled version 1.1. Unfortunately version 3.0 doesn't seem to have the roll up cumulative installation function.
I'm still on version 2.0 and two updates to that have failed to install no matter what I have tried. Personally if one of my programs didn't require .NET I wouldn't touch it with a big stick.