$300 gaming components?

Okay, I'm looking to play Battlefield 3 at high/max settings. I have a 1 TB HDD, 20 inch 4:3 monitor (up to 1024 x 768), a decent case, DVD-ROM/CD-BLAH drive, and everything else besides the core components.
I need a motherboard, CPU, video card, and PSU. All for under $300. My birthday is on September 14 and I've been browsing through LOADS of benchmarks and gameplays. I don't know too much about computers, but I know more than the average dim-wit. What I've considered is getting saving my money, but getting a 9800GT for now, then get more money for Christmas and use the 9800 as a PhysX card and get a GTX460 instead or something. I don't know. But I need PSU, Mobo, CPU, and Video card. I bought 4GB DDR3 1333MHz SDRAM a while ago and nothing to use it with.