I've been noticing that quite a few of you are having issues uninstalling a framework when partially installed or when it has been corrupted.
If you can get to the framework origininal installation package then that would be very helpful. A central location to get these downloads would be: http://msdn2.microsoft.com/en-us/netframework/aa569263.aspx
Then after you've got the installation package on your machine, execute it. what happens is that the installation will go into what is known as the maintenance mode. It will give you the option to repair and uninstall the framework.
Repairing and then uninstalling the framework in this manner normally will fix most of the issues that we've seend.
For those of you who are using 3.0, we've released a 3.0 prerelease clean up tool, which should help you put your machine into a clean state.