Get a Xenarc, not a Lilliput. In my experience and opinion, they are better than the Lilliput (especially if it is going to be mounted where there is some sunlight hitting the screen - plus the Lilliputs can break just by looking at them funny )
They are available right here on MP3Car. So is the Opus 150W, which will more than likely be fine. People here are running 3.2GHz P4's from the 150W Opus!
I recommend something along the lines of a nForce2 mATX board and an XP processor (1700+/2500+), 256mb-512mb RAM, and a non-fluid bearing harddrive (unfortunately these are becoming harder to find - i have had a fluid bearing give up on me last winter, replaced it with a sleeve bearing and it's been fine since)
From computer, you will take a 3.5mm to RCA cable, then you can just split it into the two amps.
All the other computer parts/cables are all standard
Any more questions, just ask