I've tried updating drivers (except going to nVidia reference drivers which i'll try now), and it still crashes. After updating the 4in1's it crashed almost straight away and then after rebooting the BIOS complained of a CMOS checksum error so I had to reset the settings. Is there anything (like having AGP 4x enabled) that would affect the playback?
I have also tried WinDVD however the playback was too slow and jerky so I didn't give it time to crash.
Any other ideas?