While I was making the iPod battery pack I came up with the idea of making a car charger since I bought two firewire sockets and just used one for the battery pack. So after doing a search on Google I discovered that (of course) someone had built one before. I ended up following the car charger guide from the guys over at iPoding.com.
I found an old car charger that had a 5A fuse and replaced it with a 1A one (the iPod doesn't need more than 500mA - 1A). Unfortunatly I don't have more pictures of when I built it, but you basically just connect 2 wires from the car charger to the firewire socket and your laughing (as long as your charger output is somewhere in the range of 10-30v and have a 1A fuse).
As with the battery pack, I used a female 6-pin firewire socket so that I could use the original iPod cable to charge it.
There was barely enough room for the firewire socket inside the casing for the car charger, but I managed to get it in there and had to glue the socket in place with a glue gun. Unfortunatly, I now can't open the case if something goes wrong in there. I can, however, change the fuse as it's located at the other end of the casing.
Thanks to the people over at ipoding.com for the guide.