First of all, what possessed you to buy an XBox?
Second, why would you want to shove it onto your computer?
I dont even think there IS a case out there big enough to stuff that thing in there. You'd have to put it in sideways (even that would be a stretch), which would make it hard to load games into it, given it's position, and the obvious issue of it being in your case and not easily accessible.
NZXT Guardian Case with Thermaltake PurePower 420w
FIC AU13 motherboard
AMD Athlon XP 2600+ 333FSB (Barton) with Thermaltake Silent Boost HSF
WDC 80Gb 8Mb cache 7200rpm
512Mb Kingston Dual-channel PC3200
MCP-T SoundStorm audio (integrated)
ATi Radeon 9800 Pro (it owned, until x800 and 6800)
Logitech Z-680 5.1 speaker system (integrated Dolby Digital 5.1, DTS, Pro Logic II decoding)
Logitech Cordless Elite Duo keyboard & mouse
Saitek Cyborg Evo joystick
Windows XP Pro SP1 (dont. install. SP2.)