well i have modded my xbox to emu all the old games. i work at a video game store and talk games all day. there are, i think, two halfway decent ps2 emus out there, but the roms for them are nearly impossible to find. as far as xbox emus, ive heard of them, and have even heard of cracks for the disk formats to play them on your compy, but have yet to actually attempt it, as to lack of time, and lack of desire, since i have an xbox...
try
www.xbox365.com or the links off their page, there are a couple good ones out there, i just cant remember what they are off the top of my head...