I think you should know the PCI Bus IDs for the "DEvice" sections in your
Xf86Config file. Close X or kdm or Xdm service. And on a textconsole
as root enter " XFree86 -scanpci ". In you Xfree86.log file you will find
your two Geforce cards, in the form PCI: 0:X:Y (for that one which is
plugged in the pci slot) and PCI: 1:A:B (for the other card in the agp slot
) X,Y,A,B are dummy variables here.
I've attached you a Xinerama-how-to, Probably it's also located somewhere
on your linux CDs. Well you don't need to install
Xinerama however it also could be used to check the two-cards
configuration as well. The How-To is worse reading in your case i think.
I have never set up two cards of that type on one machine and so no further