multiple video cards

I'm having multiple monitor issues. I'm trying to run 3 monitors with 2 video cards. The first card is a 7800GT 256 meg pci-express and the second card is a 6200 256 meg pci. Everyting works fine when I just run 2 monitors on the 7800, but when I enable the 3rd monitor on the 6200, the video locks up all the time. I'm using build 5308 x86 and the 87.15 nvidia drivers on both cards.
I'm a little worried that PCI video cards aren't going to be fast enough to do Vista justice. Which is sad since I love my setup... 2 dell 20" lcd's on either side of a dell 24" lcd... 5120x1600 :D
At this point I'm hoping it's just a driver issue. If not, the only other option I can think of is to switch to a SLI motherboard but not run in SLI mode. Kind of spendy, so it's definitely a last resort.
FYI, the system rating doesn't seem to be intelligent enough to take multiple video cards into account. It always wants to count only my 6200 (rating 3). When I disable the 6200, it uses the 7800 (rating 5)... the rest of my system is at level 5+, (3.2ghz dual core, 2 gigs ram).
In the mean time I'm down to 2 monitors. The performance of the UI is still pretty sluggish. I guess I'll try again next build.