Not my first attempt but definitely one of the easiest to reproduce...

I've been mounting Macs in my spare tyre, baby. The first Mac I tried was a Mini, but I got sick of waiting for it to start up, if it even chose to start up at all. So I switched to a 12" Powerbook which fits so perfectly you'd think it was designed for this exact purpose. 512mb ram, 80 gig disk, split or mirrored external display, 802.11, bluetooth, usb2 etc.

I've had a Lilliput 7" mounted in my dash for some time now, with the early designs of the wrx bezel. The old model I have is hard to see in the day but looks fantastic at night. And here's a tip, the touch interface works even when the screen is not powered.

I had bought and adapted a car laptop supply for the Mac mini at 18V. Fortunately it also supports the 24V required by the Powerbook. I tried an inverter but it destroyed the audio. And I don't like the idea of 240V AC for every day use.

Originally I had a PC hooked up. Then a PS2 for a little while. You can find my touchscreen driver on the opensource ps2dev sites. Then the Mini. I stayed away from rewiring the Mini and tried to use a 2nd battery to keep it awake long enough that it would not shut down. And if it did shut down, I had the restart from power failure system preference ticked. Problem was the car laptop adapter drains 12 watts no matter what. The 2nd battery would go flat in less than a couple of days. And most of the time it wouldn't recover from power failure.. sometimes it would, if I slowly turned the ignition between modes, bleah.

Since I had to sacrifice my headunit I opted to bolt an Alpine amp under the passenger seat. I then have usb running from the boot to the dash, where I have a usb hub, connected to a Griffin iMic, noname GPS (off ebay) and spare cable, that I use to plug in my phone (I intend to mount a socket in a button tab, easy enough with the Dremel).

The Griffin iMic is wired to the amp and a car kit microphone. Music is A-grade++. The downside is, with any sort of decent volume the voice recognition starts to break down.

I recently wired a Woofer into the boot. Is awesome.

The wiring of the laptop itself is a bit ghetto. But it's very quick to get in and out. It sits on top of several soft fabrics and anything I could find to act as a cushion. But you wouldn't know it's there just by looking in the boot:
http://public.box.net/matt

So software...
For a long time I was just using Coverflow. It's very cool. But very hard to control with the dodgy stock driver - some friends couldn't even get it to play the album they want, currently at the front. I ended up writing the driver from scratch. It surprisingly took a lot longer than the one I did for the PS2. I'll give it away for free. Be warned it's hardwired to my calibration settings... if anyone wants me a preference pane to calibrate I would be happy to develop this, for a financial incentive.

Nowadays I'm using iTunes with it's built in Coverflow, surrounded by internet and custom dashboard widgets. My favourite iTunes visualisation is Eyephedrine. Try it!

I registered to Google Earth so I could use it's gps function. But it doesn't seem to support my dodgy ebay gps. So instead I got Ge2GpsX which bridges data from gpsd to Google Earth, no registration required.

I have a shell script to relay filter and relay gpsd data to TomTom running on my phone for navigation. I have a bluetooth gps dongle (Navman) but it needs to be turned on with a button press, not cool. I used to use SmartST but TomTom is clearly more awesome.

I had too many difficulties running the resolution at 800x480. Even when I got it reliably going, many applications assume a height of at least 640. 800x600 looks great, but if anyone does want to do 800x480 then DisplayConfigX is the tool of choice.

For the future...
I hope to have a usb socket wired up. Use as a car phone kit. Auto wireless joining and routing through DNS, mmm. Cameras. Sensors. Enclosure that can accommodate woofer & powerbook. Radio (waiting on digital). More widgets.