GMA950 is a chipset... Ultimately you need slots on your motherboard to support add on video cards. The Geforce 5600 is from the way way back, 1st gen DX9 cards. I'm not even sure if there is a PCI-E variant of that card.
Either way, you need to know what slots you have, and what slots you want to use (PCI-E, AGP, etc).