How do I change a disk partition map scheme from MBR to GUID Partitions Table?
Ok thanks for your help, but I solved the problem on my way, here's what I've done:


Backup everything important to an external Harddrive
Inserted the Mac Installation Disc and ruined there the disc utility app.
I removed everything from my HD and it was GUID-Partioned.
Now I just installed Mac Os X 10.6.2 and updated to 10.6.8
Now I could run the installer of Mac Os X Lion without any problems and as a benefit of the whole thing, I started with a brand new Mac Os X Installation, without any trash in the file system.