I'm currently working on a CarPC install in my LS400.
Here's a full diagram that I whipped up:
I'm currently trying to figure out all the fuse sizes (blue boxes) so I can get the whole thing wired up. The only one that's in there right now is the one coming from the battery. Let me know if you guys have any input.
The relays in the bottom right corner switch auxiliary inputs between the stock cd changer and the pc.
Pics coming soon.