Confusingboat 
THIS:
Is exciting. It's meant for 06+ Hummer H3 direct replacement, but since GM is awesome with their interchangeable parts it's also a direct fit (possibly some VERY minor dremmeling on the sides) for the 04+ GP. This makes adding a carputer even easier.
Here's the plan:
-Direct replacement touch screen
-Tiny ass computer with good specs
-250gb laptop drive I have from my old Archos that broke
-2gb DDR2 RAM I have laying around from other computer shiz
-Super tiny speaker amplifier to mount behind the touchscreen
-DC power supply
-Centrafuse frontend software running on TinyXP (or even MicroXP if I can get it to work with it) for maximum minimization of boot time
-Some custom background software I'm going to write to have my car media library sync with my home library while it's sitting in the driveway (wireless 802.11n ftw)
-Bluetooth dongle I already own
Total: ~$700
Not bad since my previous guestimation about 10 months ago was roughly $1000+. Upgrades can be made later, such as a USB GPS reciever (~$30) and a USB HD radio adapter. Also the touchscreen can be upgraded with a capacitive touch controller whenever -- they're all compatible with XP. Imo this completely dominates any head unit you can get, as long as you don't mind waiting a little bit longer for the unit to boot up. There are many optimizations that can be made for shortening boot times though, such as enabling the no GUI windows boot, don't display POST (allows it to POST faster), etc.
Update: New PC choice for next-gen Ion graphics instead of terrible integrated Atom gpu. Price add $100 -- **** technology
