The Sempron (socket A) is the same as an Athlon, but with a slower FSB and less cache. Despite what people may think, they're not that bad off. They also have nothing to do with the fill rate.

Your problem has to do with a few things.
First, the Radeon 9600Pro was a great card in the day, but it's been a few years, and it's simply not stood the test of time, as is typical with video cards.
Second, 3DMark is quite tempermental to things like chipset drivers being installed. Poor scores have been linked to this, although in actual games, this hasn't meant a damn.
Third, the resolution used will also have an affect.

If you've run actual games and not run into problems, I wouldn't worry. 3DWangMark simply isn't a good test of your graphic capabilities.

2003 is a bit newer, and I would think that the more advanced tests in that suite would hit harder on the card than on newer cards.

2001 is more appropriate for your card.