I think you're right, your 3Dmark03 score should be 7300-7600. My friend's set up is almost exactly like yours and he gets ~7400 scores.
The only thing I can suggest is set you RAM back to 200MHz. you'll probably have to reset your Latency timings as well. That might gain some points. (Although i doubt it will gain 1000 points)
Also, it is my understanding that the 3Dmark03 program is mostly a test of your video card, not the entire system. So, in my opinion your issue is with the video card.