I've been doing this for a while now. Its great.
I use a hawking wireless access point for my truck, it has an RJ45 socket and takes 5v DC. I bought a cigeratte adaptor. Inside I use a PCMCIA card to either my laptop or my desktop machine (through a PCMCIA adaptor). Its pretty cool being able to type "ping truck" at the command prompt.
I got the wireless gear from frys. ~$250 all up.
I had been leaving the access point on all the time (at least when the vehicle was stopped (don't want to grow any more tumors), but there is a
bug in the 2.0b3 and higher versions of emplode /player that causes the player to die abruptly if the timeout is too high. I was using 20,000 seconds and I havent found the new max value yet.
Good luck
Peter