xbox can emulate gameboy, nes, supernes, sega megadrive, n64, ps1, arcade games and a few other simple consoles but not ps2! ps2 architecture is completely different and i doubt it will ever be emulated on xbox.
The xbox has a harddrive and I'm assuming that when you say it can emulate these consoles it's just using one of the ready made emulators on the xbox platform. Nobody has been able to emulate PS2 yet. I think FFX works a little but for the most part, games just load the intro screen and that's about it.