I don't understand how the VS 2008 plugin can be related to my problem.
I build the Qt libs and binaries (Designer.exe etc.) from the sources without any errors. So the Designer, Creater etc. should work now - but they don't work.
Why would a Plugin for VS magically solve this problem?
Edit: I just installed the VS Addin and then the VS2008 package. I installed the VS 2008 package to D:\Qt and all the Executables in D:\Qt are running (the designer.exe etc.). I also tried to make a little sample application in VS 2010 and it also worked.
The Binares in the folder where I manually built everything still don't work and I just deleted them. I still have no idea why they did not work even though everything build without an error, but since I can develop now I guess I should not care