A lesson to be learned, perhaps? Your system is very similar to mine, I'm running:
Athlon XP 3000+, 2 x 512 pc2700 not so fast
ram 
, with a pny geforce 6800 gs 256 mb agp...
Running 3dmark standard settings (1024x768, no AA, optimal filtering, vs3.0, ps3.0), I pull a score of 5155 with pipelines unlocked on my vid card,
oc'd to 380/1060...stock was about 4217, so the unlocking and
oc'ing had definite benefits, and yes, oblivion is the current game of choice, but my framerates arent quite as high as yours....crappier
cpu and not as much video memory, most likely!
-Ashley