Well I forgot to mention that I already removed the GF2 and put back in the Ati Rage Pro PCI.
So it's not that D3D card switching problem. The switching between PCX2 and Rage works.
The crashes with the default Matrox 126.96.36.199 driver with PVRHAL + D3D seem to be independent of the card. It is just some misconfiguration of the PVRHAL itself.
In this case f.e. Final Reality crashes always to Desktop after the Tunnel scene before the rotating Spaceship scene.
3DMark2000 crashes to desktop as soon as any 3D scene should be shown... (I could continue here...
Another oddity is, that I have to boot Win98SE always twice. So on first boot the PowerVR API is not loaded (no exclamation mark in the device manager though). If I reboot Win98SE holding shift everything is there.