If you're gonna be playing Oblivion, don't get a Celeron. They take ages to boot up, and close down, and they're just plain slow for gaming. I had a 2.4GHz Celey and I hated it.
well, its to late for that. i already have a celeron. and i realize now they suck for gaming, but there's not much i can do but get the most i can out of it.
A Celeron D is pretty much the same thing as the older Prescott P4's. Since you have a lot of memory just get a good video card and you should be able to play Oblivion on medium settings (maybe higher since Oblivion is very graphics intensive.)
Get atleast a 6600gt if not something in the 7000 series.
The thing is that a Celeron has a 533MHZ FSB and an Extremely small L2Cache think of your front side bus as a highway between two Citys 1 being your Hard Drive or CD Drive, whatever is accessing your processor. City 2 being your processor in itself. Now, shure your processor can handle 3.2GHZ at a time but the FSB limits the amount of traffic to your processor. Now my AMD Processor has a 2000MHZ FSB (No joke it is on their website, it is because of HyperTransport Technology read on their website about socket 939 Processors) so the bigger the FSB and L2cache the better and metaphoricaly speaking the faster your processor.
if you have a choice between a 7600 and 6600 geforce, choose the 7600. your best buy would be a BFG graphic card though. their cards are of the highest quality. plus they all come overclocked and still under true lifetime warranty. also there is a better chance that you could unlock the hidden features of a BFG card because they use good quality chips. so that means you could buy a 7600GS and unluck the hidden features yourself and end up with a 7600GT at no extra cost.