A friend of mine scored a quad 2.66 with a 20" ACD for $900! what a deal. He has 4 monitors he wants to connect. I have an old 64mb video card from a G5 I want to give him if it will work. Will it work in the mac pro?

The graphics card needs to fit in a 16-lane PCI Express slot
http://www.everymac.com/systems/apple/mac_pro/stats/mac-pro-quad-2.66-specs.html and needs Universal drivers.
Are you sure the graphics card is from a G5 and not a G4 as searches point to that this card belong in a G4 and is a Nvidia Geforce MX with 64MB.
Can't you give more information about the card?
But most probably no.
EDIT:
Upsy daisy.
It looks like a PCI Express card, so it would have to be a G5 card.
Regardless, it's Open Firmware, not EFI, and can't be used in a Mac Pro, even if there were drivers.