Your monitor res may be 1280x1024 or 1600x1200 but 3dmark05 doesn't bench at that. The demo version ( which is what everyone here has) defaults at 1024x768, so that's technically what you're benching at.
Honestly considering the CPU I figured you'd get higher.
I just benched my 6800GT with Ultra speeds...well just a TINY bit better lol at a insane 401/1101 lol.....a whole 1MHz on each
Anyway I got 5,410 and I'm on a 2.6GHz Athlon XP-M and 1gb of 2-2-2-5 timing RAM.
Your card is perfoming right on though....I assume that extra 100 points is coming from your processor, but yeah......it's definitely performing exactly where it should, soooooooo now OC that beast