I fixed my .Net installation issues. It turned out to be an access problem. I read the following two pages:
Also installed the windows installer 3.1 and the WIC installer.
For me it turned out to be an access issue, but the solution in those pages put a smile on my face. It's a good trick to keep in mind, I've seen a lot of unresolved cases like this on the net, and had to dig to find this solution.