Upgrading cpu,gpu,both, or new comp

This is my current situation. I am a gamer and I want to play a game called Rift. However my computer is outdated and I get very bad framrates on it. They vary from 10 to 70 depending upon where i am. However, during combat, it averages about 25. This is on all of the lowest settings. These are my specs: e5200@ 2.8Ghz 4gb ram geforce gts 250 1gb video card. I have talked to some people and have received different opinions on what to do. If I wanted to spend about 200 bucks to get me by before I buy a whole new real computer, what would make Rift atleast playable. I was thinking for the gpu a new gtx460 1gb ddr5 for 150 to 200 dollars on newegg. I already have a 650 watt psu. For the cpu, perhaps a new core 2 quad. Rift is both cpu and gpu intensive. Inside the games benchmarks it said my gpu was holding me back more than the cpu. So if Im not going to get a new computer, would an overclocked gtx460 help me out to get by? Also, i was told that despite having the lga socket 775 slot for a core 2 quad that it could be rejected by the manufacturers bios. The system is a gateway. At this point i do not want to by a new computer just yet. Thanks