Basically, the more pipelines you have, the faster your card is. Pipelines are actually more important than clock speed in determining GPU performance. You need at least 8 pipelines in this day and age to get acceptable performance in games, which cards like the 6600 GT have. Today's high end cards have 16 pipelines, and pretty soon 32-piped cards will be released.
With my Radeon 9200SE I get around 4400 on 3Dmark03. It also has only 4 pipelines. The Integrated Graphics Media Accelerator 900 that originally came with my system also has 4 pipelines. The only difference I believe between the integrated and the 9200se is the graphics card doesn't use the system ram. The X300 is probably pretty equal to the 9200 the only difference being it's PCI Express.
On yours or mine? What are your systems specs? I have 1GB of RAM and a 3400Mhz CPU. Using the Catalyst Contro Panel I put all the settings to Performance instead of Quality. When I put them all to Quality I only get around 2200 in 3Dmark03.