Koen Verbeeck (11/15/2013)
Found the issue. Found a log file in \AppData\Local\Temp, called SqlSetup.logMost important line was:
Error: Cannot load .Net security policy file 0x80004005
A quick google search told me to reset the .NET security for the machine.
How to: Return to the Default Security Policy Settings Using Caspol.exe
Well, that's a little scarey. Thanks for posting the solution. I've filed it away in the memory banks, since it'll help if we get to 2012 some day.