I used the latest wheezy netinstaller of 31.07.2011. A lot of stuff was fixed. It now recognizes my USB stick as 'CDROM' and installation was successful. I did not see any errors. The installation was a standard installation with "install" as option and just a base system. I will do some more testing in the coming time to see whether it can run fine with a preseed.cfg file. Good work everybody ! Regards, Jeroen