There are great guides to overclocking at
http://www.tweaktown.com. You can at least overclock your video card, which will get you the 3DMark score you want. But with a Dell I don't think you have bios options to overclock your front side bus/cpu.
Also their "Reformat to Relax" guide to tweaking XP will get you 500-or-so 3dMarks alone.
And if its just for the score you get about 500 points by using Riva Tuner (which is also great for overclocking your video card) to set Mitmap LOD bias to +3, turn off W buffer, and disable 8bit texture. Make sure Antialiasing and Ansiotropic filtering are off. You'll want to reset these to default afterwards because they drastically decrease graphics quality.
You can fix your refresh rate with Riva Tuner too (set it to your monitors max refresh rate).