I'm also doing something like this...
I'm using a Linksys WRT54G v2 with OpenWRT and a Arduino with the router's serial interface connected to digital pins 1,0, and GND.
I seem to have acquired a barbie jeep over time.. I might gut it and make my own base for it. Using the parts from the jeep.
Links for reference:
http://www.jbprojects.net/projects/wifirobot/ (not mine)
http://www.ladyada.net/learn/arduino/lesson4.html
http://i45.tinypic.com/1zv5xf6.jpg - random
http://arduino.cc/en/Main/ArduinoBoardDuemilanove
http://robostuff.com/diy-projects/routerbo...control-servos/
http://owfs.sourceforge.net/WRT54G.html#hardware