Xbox in the car?

You can't completely insulate the XBOX, or you get no heat dissipation, and that will blow it out first.  The hard drive is the MAIN issue here.  THe new car MP3 players incoporate a new Hard Drive system, and they are in the new head units.  Some consideration must have been taken for people with VERY loud audio systems, or the same failure would occur in the hard disk in the MP3 unit as you are asking about.  In fact, there is a CD Changer style MP3 unit on the market today, and looks pretty simple.  As for anti-shock design, didn't really see any.

YOu can strip the Xbox of it's shell, and make your own.  The Xbox is heavy for a reason, so you can't pull it off the TV stabd while playing it, the controller's 1/4" round plug will disconnect first.  Nothing in the Xbox is as heavy as the entire unit is. 

I don't think you have a problem unless the XBOX is mounted on TOP of your speaker cabinet or in very close proximity.  I have 400Watts of bass, and the changer is right behind the cabinet.  The CDs never skip unless I hit a bump hard enough, never during music.

You may want to place some material UNDER the Xbox for shock, but vibrations shouldn't be the KEY issue.

I have seen pictures where people completely gut their Glove Box, and place PCs and Laptops inside it, as an MP3 player.  The Xbox as it is will not fit inside a glove box, but removing the glove box and buillding a platfoem woudl be neat.

That, or take the Xbox apart and mount the parts IN the glove box.