What processor and video card should I get?

I downloaded Battlefield: Bad Company 2 and discovered my computer could not handle the game. I only have 224mb video card (Intel 82945G) and a Pentium 4 3.0 GHz processor on Windows XP. The needed for the game is 256mb video card and Duo Core 2.0 GHz processor (recommened 512mb Video, Quad Core 3.0GHz processor, and Vista or 7). I have enough processing speed, but not the duo core. I don't have much money to spend. I don't mind purchasing off brands and I am a fan of Amazon (although the best deals would be preferable). Any ideas on what is best to purchase and what else to consider? Also, can I have 2 processors and video cards on my computer at one time if I have room to fit both? What complications would exist there?