Mobo = Motherboard.
You could go to Crucial.com and use the "Scan My System" button on the main page. (Only works with Internet Explorer or with the IE Tab extension in Firefox.) Click to agree to the Terms and Conditions and let it run. The page it comes up with RAM options... but on the left side of the screen, it has a bunch of text boxes; check the one that says video card, and un-check the others. Then, click on the ones that it shows, and it will tell you if it's AGP or PCI.
AJ