Yet mentioned something i forgot, power supply, were you able to get any information on it?
computers seem complicated, and deep down in all the code it IS an endless fuckin maze, but when it comes to hardware its ridiculously easy, i was doing this stuff in the 8th grade, youre a grown man so you shouldnt have a problem.
and i can tell you right now the all geforce 7900's were made only with PCI express, so there you go, thats your slot type.

last thing to check would be RAM, find out your motherboard brand/model, research it and you'll have no problem finding the right RAM sizes