New computer dude, a 2ghz is seriously old and busted.
For reference, I was running sins on a dual 3.2Ghz xeon box with a 7800gs. Sins ran great till late game at which point it chugged. My motherboard is now defunct, so I'm running on a 3.0Ghz P4, still much much faster than yours. I have twice the ram, and the ram is twice as fast.
With half again the processing power you've got, and one of the best AGP cards you could possibly put in that box, I still can't run it anywhere near as well. It's actually been a good thing for testing functionality as quite a few abilities I had set up no longer worked. That system you've got will be misfiring left and right on event triggers.
A five year old box would be pushing it, that one's an eight. Save yourself the hassle and spend $800 putting something decent together. You'll spend more money for lower quality components trying to upgrade that thing as far as it will go, and still have an old and busted POS when you're done. Shell out for a decent AM3 setup with a mid range video card and you'll have flawless performance on a light budget.
