If you want to run Battlefield 3 on Max or high settings and have 30 FPS. you need a Strong video card, i would say, AMD CPU, Geforce Video card, 8GB ram, 600W or higher power supply, Most new video cards should have a White Plug (DVI) Blue Plug is VGA. if you want it to look good, get DVI or HDMI! i say pick AMD CPU cause they are alot cheaper then intel...alot, i say pick Geforce because you get a good idea of what you can run from them!
GeForce GTX 650 Ti | GeForce Mine, shows me what i run it vs an older card. I know Micro center has some good Bundle deals, like buy a CPU, motherboard, ram and get Blah amount off. never a bad idea. you can also check out
Newegg.com - Computer Parts, Laptops, Electronics, and More! or
TigerDirec*****m - Electronics, Tablets, Phones, Office Supplies & Video Games, or even
iBUYPOWER Gaming PC: Custom Gaming Computers and Laptops ebay would make stuff cheaper but a chance of it being broke or something like that.
PS, if your computer screen only has say blue (VGA) im pretty sure you can buy a little thing that takes it from VGA to DVI.