I think T. Payton is absolutely right about the Events and Projects.
With ‘Event Manager X’ I disabled all events and projects and worked only with the project and event I needed.
All my problems we’re gone.
I can work with original media and no wheel of death any more.
I’m working with 6GB RAM and an 2008 Mac Pro on Snow Leopard.
So the solution for me: Only use the events and projects you need at the moment and disable the others with ‘Event Manager X’