This is a decent head unit but its just under $300.
http://www.sonicelectronix.com/item_33722_Clarion-VZ401.html
If you wanted to hook up a computer you could get one of these
http://www.amazon.com/HDE-Adapter-S-Video-Cable-Video/dp/B000Y7T5UU
I thought about doing the same thing so I could load a ton of music on the computer and use the wifi tether on my phone to give the computer internet so I could use pandora or whatever else I wanted to do. The problem with that adapter cable is the resolution is absolutely horrible, its usable, but horrible.
I am very interested in doing this in my own truck but I have little to no experience in working with fiberglass or bondo.
What I thought of instead which would only with the 88-94 dash without major modification (95-99 dash would require major modding) is using a regular radio in the location under the vents in the center of the dash and using this
http://compare.ebay.com/like/350720227695?var=lv<yp=AllFixedPriceItemTypes&var=sbar in the stock radio location above the hvac controls. You could get the plastic "pocket" that comes with that radio kit and modify it to accept the tablet then hook up the audio out on the tablet to the aux in on the radio. This way you wouldn't have to sacrifice resolution, you would have a operating system meant for "on the go" applications, and you could take the tablet with you when not in your truck of needed. Another added feature is that you wouldn't have to hide a power supply (which you would need a decent sized unit to run the computer) and a computer. Also it would suck to have to wait for your computer to start up and shut down every time you get in and out of your vehicle and/or turn off or on your power supply.