Help with dual video cards

I have been using dual video cards (each a dual output card) with 4 monitors for many, many years, across 3 different PC's and many combinations of different cards. Never had a problem until now.

I tried to update my primary card from a 256MB nVidia GeForce 6 series to an nVidia GeForce 9 series PCIe with 512MB of DDR3 memory. This card works great on its own, but I cannot get the nVidia GeForce MX4000 to work with it. The MX4000 and the 6 series worked great together, as has every other combination that I have ever had in the past.

When both cards are enabled, I get a BSOD prior to the login prompt. It goes by so fast and restarts on its own that I cannot read any of it. I have tried switching the primary card in the BIOS (making the MX4000 the primary) to no avail. I have tried every method of installing/un-installing hardware and drivers I can think of with no joy. I have tried using older drivers and the latest drivers for each card in various combinations, no luck.

Is the DDR3 incompatible with DDR2 in the system? Any other ideas, thoughts or suggestions?

Thanks....!

 

Sorry for the long delay...
I have tried a complete re-installation of XP from scratch in an attempt to get these 2 cards to live together with no luck, so it would seem that Arie is correct - they just are never going to play nice.

So the question is, any suggestions on how to find a card that will work with it without going through a long trial and error process?

Again, it's an nVidia EVGA 9800GT, PCI-E 2.0, 512MB DDR3. Whatever the second card turns out to be, it does not have to be a terribly robust piece of hardware. All the movie editing and 'hard' work is done on the 2 primary monitors.