Since I play Oblivion and F.E.A.R., can actually help you a little...
You will need a faster CPU (relatively cheap compared to the rest of the items).
Depending on your motherboard:
1. Go with a nice AMD; I have a 3700+, but you can easily buy dual core cpu's for a damned good price now (basically you and I both need to upgrade in this department).
2. Ram - get 2 gigs; I prefer OCZ (lifetime warrenty + low latency) - the lower the latency (the numbers on the ram) the faster it performs. And never use one stick, always pair them up; a one gig stick will be slower than two 512 sticks together.
----Now, your motherboard will limit how much ram you can use effectively. If you have an old board I would suggest upgrading, because the amount of ram you can use is dependent on how much your front bus can handle. If your motherboard can't use all the ram, you are wasting money.
3. As for cards...I only know about nvidia - I have a 6800 ultra which is basically just a tad bit behind the mid 7000 series. But I feel lag when playing oblivion on uber high settings. If you want a PC for gaming, you will need to get a card with at least 512megs of ram built in. This means go with nvidia 7000...or 8000 series. Either way, you will be spending a lot of fucking money on a card. Maybe some others know os some good cards for a good price.
If you over-clock your system then you can go with a little lower specs, but I don't rec it, seeing as if you fuck up you can destroy your system entirely (I've seen it happen three times..so many delicious tears)
Try Newegg.com for everything - pretty good selections, and when they have sales....oh my oh my oh my. You could also try Fry's, but whenever I go there, there is no sale....just myths surrounding one
