you can get a gig for around 60 bucks.
Or you can go to the dell outlet, and pick up a fairly nice computer for around 300.
As someone else stated, you'll need a computer that can process at around 8-10x the speed of the original machine. Although your current specs shouldnt have too much of a problem running a DS emulator "in theory", in practice it won't be happening anytime soon because, again, like someone else said, the DS emu's aren't optimized.
I tried playing windwaker on my computer
amd 4000+
3gb corsair xms
Asus 7800gtx
and I got a staggering framerate, which is too bad, since I spent all my money on a PC instead of a cube