2008 Mac Pro dual quad core 3Ghx originally with the ATI X1900 on two monitors (a 20" and a 30").

I just added 8 GB RAM (to 16GB) and I bought the ATI3870 (PC and MAC edition) as well as the NEC2690WUXi monitor. Of course, I had to upgrade from Tiger to Leopard because there are no drivers for Tiger for the ATI 3870. The 4879 wont be ready for at least another 6 weeks I'm told... So, after spending around $2k, I have had nothing but problems.
There are video issues in Aperture and even with the Display function on system preferences whenever the third monitor is plugged in or when I try to use the x1900 and the new 3820 at the same time.

Does anyone out there have a working system with these two video cards? Any hints on how to make it work?

One of the ATI engineers told me today that the system does not have enough power to run both these power hungry video cards. Does that sound right to you, or do I have a bad card that I should return?
Has anyone had to put a larger power supply into their Mac Pros to get two high end video cards to play nice?
Thanks for any suggestions!