From what I know (it probably isn't much 😉) but I think it will be quite some time. First off you need to have the computing power. You may say "well the my PC has a 2.2P4 + GF4, it can handle it" but you have to remember that the games on xbox run @ TV resolution, not 1024x768... Also, no one has found a way to rip the games, thats going to be a big issue as well.
True that PS2 emulaters are starting to show up but PS2 games were able to be copied from day one... its already been 5 months since xbox was released and there is still no way to rip them...