0) I'll try that ..
1) No, i haven't upgraded my mainboard .. I cant remember it at least (its five years old ..). I'll check if there is an update available and install it if i can find an old boot disc
2) At the moment there is no specific application which triggers the crash i think. The last time it crashed while i was posting on this forum (with firefox).
Thanks for the reply.
Edit: The NvAGP Option doesnt change anything.