I am currently doing that very install into a BMW 318 TI.

There are a few minor things you may want to consider while doing this install.

Chip the board with a Matrix chip
Upgrade the BIOS (EvoX is a great call on this)
Upgrade the hard drive with a 120 gig drive
Switch out the DVD ROM drive with a slot feed drive to eliminate the tray with the stock DVD drive.
Upgrade the IDE cable to a 133 round wound cable for flexibility and the max length is 36" from the mother board.

In doing this basically you will be pulling the entire XboX apart and removing it from its case all together, although in the Accord this is unnecessary as it will fit in the Accords glove box as is.

You may also want to extend the wiring from the control ports so you can locate them at various points but just so you know they are grouped together as sets of two and seperating the two will result in some issues.

The eject button and the power button can be remote located rather easily also....but you will need to extend the wires from the back of it to the Motherboard and if you end up switching out the DVD drive you have to do some custom wiring to get the new DVD drive to accept the eject controls.

As for powering it that is simple a power inverter takes care of this. In putting the chip and the upgraded BIOS in the XboX you will no longer be able to play XboX Live but you wil be able to burn games to the drive so you can just rent them, rip them and return them resulting in faster load times and smoother gameplay. You can still link them together for multiplayer games as normal but you get the added benefit of being able to play both MP3 format as well as movie files in DIVX format which is something you can't do otherwise.