What shall i upgrade first on my pc?

To start, if you are looking to play high demanding 3d games then you need to upgrade the MoBo and processor first to at least a p55 and i5 (quad core) if not higher. Then go for 4 or more gigs of DDR3 1333/1600mhz memory and a better video card (gtx 260 at least). This is all just generalizations though. All parts can be found at www.tigerdirect.com or www.newegg.com for competitive pricing.