Check your Add or Remove Programs list to see if .Net 2.0 is listed. If it is, try to remove it from there. If you are unsuccessfule, use the MSICleanup utility from MS. I cna't remember the exact name (Windows Installer CleanUp), but use it to get rid of the .Net 2.0 existence to Windows.
I had this happen before, but it was only when an application was trying to install .NET 2.0. It was partially installed, so I had to get rid of it manually, then get the install from MS. It should be part of their Windows UPdates along with any service packs for it...not sure if 2.0 has SP's, but I know 1.1 does. Good luck!!