Thanks for your quick replys.
All computers i have testet it on have Windows 7 64 Bit installed and have newer Nvidia Cards like Gtx560 and Gtx580.
All Systems are up to Date, DX is up to Date, Drivers too.
All Settings in the Nvidia Panel are set to default Values.
Vsync is enabled in the Application settings in my Project and works like it should in Window-Mode. I am trying to run it at 1280x720 px Fullscreen but the Problem is independent from the Resolution.
To bad i can not post a cap because its from a commercial project we are working on. I have crated a blank cap and startet it fullscreen and the Problem does not exist there. So what can cause Vsync not to work like it should? Its like switching on and of rapidly. Framerates changes from 60FPS to 600PFS ten times a second.