So did you do the BF1942 tweaks as suggested & see what happens?
That might eliminate any issues the BF1942 might have with the NVidea drivers If that game doesn't mess with the latest *1.00++ series of drivers??
From what I've read & seen posted I understand that the game has to provide inherent SLI support or issues will likely (may) result. Maybe BF1942 doesn't like (provide support for) the drivers you have??
Why not try the tweak for BF 1942 & see what difference it makes (if any) - on 1 of the machines.
If it is NOT system related - as you suggest, & have seen other games run well, then it must be the game(s) themselves - make sense?
Maybe with all your soft/hardware config you can't run the 2 games at 1900X1200?? Perhaps the "hacks" might also cause a conflict, with YOUR rig?
Here is a guy having similar problems (oct 29, 2005)
Link
Similiar CPU's & similiar MB's - but with ATI cards --- Hmmmm
Sometimes it can be the wierdest conflict.