I got a 9800GT and a 600watts PSU but the problem is my processor, its only 2.8ghz pentium d 820 single core. it gives me problem with my FPS. i know its bottleneck. planning to buy a 2.5ghz dual core, is it worth it?
It depends on how much you're paying for it. If it's below $40, sure, get it. But really, for around $140 you could get a new motherboard + 4 GB RAM + Sandy Bridge CPU which would be WAY better than E6600. Of course, that price is if you're in US. If you're from somewhere else, prices will be a bit higher (around 20-30%).