I have installed a computer in my 2004 S80 2.5T AWD.
A couple of things:
1. Computer position
I have put my computer in the glove compartment (I use a VIA EPIA MII1000 motherboard with a standard 3.5" 160GB hard drive). It totally fills the glove compartment, but you can run wires from it to the central console.
2. Screen position. I have used Proclip USA clips to fix the monitor. This does a really clean install without having to break anything.
3. Getting sound from the PC to the radio. There you are out of luck. There are devices that does that (I use the SPECUSA VOL-11 - designe with iPod in mind but giving an external Aux connector too) by connecting directly in the CD changer port behind the radio, but it is not compatible with volvo navigation. I think you're stuck with either and FM emitter (that uses the airwaves to broadcast on a specific channel) or a wired FM modulator (that put itself between the antenna and the radio, and emit on a specific channel - you will need special antenna adaptors). The wired ones are better than the airwaves ones. DO NOT USE CHEAP STUFF FOR THIS. This will be the weakest point of you whole system. The best source of information for this all of is this board: Swedespeed tech forums
My car is presently in the repair shop (a kid crashed in it a couple of weeks ago - 10K$ of dammages - a brand new car !! (*&%(*%(*%) and I do not have pictures of the glove compartment, but I have posted this description of my installation in another thread .
Any question you have, I'm here ;-)