A 7950GX2 Problem

Okay, first things first, here is my PC:

CPU: Pentium D 820 @ Stock 2.8 GHz
RAM: 4x 512mb DDR2 533/PC2 4200
GPU: 7950GX2 @ Stock 500/1200
MB: ECS 945P-A Revision 1.1
P/S: Ultra 600Watt HERE
+extra stuff that shouldn't matter for this topic anyways

The problem is that when I am playing Oblivion, I get about the same frame rates as my old 7800GT, and its real slow for what I paid for. BUT, on the other hand, Call of Duty 2 plays at a much higher fps than my 7800GT ever did. I have the latest drivers for everything, and have even updated my motherboard BIOS, but I'm still confused.

Any help would be GREATLY appreciated!

Thanks

Oh I forgot to mention sorry. I am running on 1600x1200 (a major reason why I got the card). I'm thinking that the CPU might be bottle-necking the GPU cause of the power Oblivion requires, since other games like Call of Duty 2 run way faster than my old 7800GT, but those games aren't CPU intensive.

Well I think I'm gonna go for a brand new PC (except carrying on this graphics card ), since that was my plan when Conroe came out. Anyways, I think its time to upgrade from this crappy CPU and high latency RAM. Now the only think to do is get my parents to put forth the money, but thanks to good grades and some awards I might have a 25% chance =)