System Shock (the original game) might run under DOSXBox, as it's a DOS game, though I don't know how well it would perform. System Shock 2 won't run as it's Windows only, and it can't be ported as (to the best of my knowledge) it's still closed source.
Actually, System Shock 2 *might* be made to work on an XBox, if you use Linux and WINE, or some other Linux solution, but I can't help there as I know nothing about Linux, sorry. If you try then please let us know your results - aparently Half life has been made to run on an XBox under Linux and WINE (or whatever), but I've not seen it.
Good luck.