Frag Maniac :
You won't need to upgrade the MB as long as it has a Pci-Ex slot, but as mentioned you WILL need to give a budget before I can recommend a GPU. So far I only know you have a 635w PSU, with no clue as to what you can afford for a GPU. It would be better if you mention the brand and model of PSU so I know what quality it is.
If you don't know how to look for brand/model of PSU, lots of free software tools will show it, like HW Monitor.
Hey, sorry for the very late reply i was away.
My Budget: $260usd
Following are the WHOLE specs for my computer:
Intel® Xeon®E5-1620 Processor @ 3.6 ghz
2 x AMD FirePro V7900 Graphics Cards
8GB DDR3 Ram
Dell motherboard, with two Pci-Ex slots
the power supply is unbranded, and is sort of integrated, 635w