I think your confused on what the xbox is...ITS a console not a PC. It might look like a PC, but it's systems cannot ascept a "Windows CD" to boot. Pretty much everything on the inside is proprietory, and it would take a lot of work..if not impossible to convert to a MAME machine.
I would hope that someone would develop a MAME version for it and release it, but don't hold your breath!
Questions:
1. No
2. No
3. Standard DVD, but cannot read CDRs.
4 . Power supply is a special ATX connector, not standard ATX.
5. Memory is directly soldered on board.
6. No keyboard or mouse connections inside, just special USB connections for the controllers. No and you can't connect a USB to it!
7. N/A
8. 8 gig proprietary OS
9 As big as the case.
10 I guess, with a lot of cutting
Your better off buying cheap PC for less than $300!