do all original Xbox games work on Xbox360?

or do only certain ones, or none?!

i really want to play on Metal Gear Solid & i havnt got enough money for a PS3, plus i never had a PS2 or original Xbox so i couldnt play the second MGS or the third, so i was thinkin of buying them for Xbox & playing them with my 360

just wanted to know if they'd work or not, cheeeers