You would need something to interface the output from the RF receiver to the PC.
You can search google/mp3car and find tons of parallel, serial, etc IO/relay boards, but I'd suggest USB and a search of the board shows Phidgets's USB stuff a popular way to interface. The outputs on the reciever would be tied into the inputs on this board. You can probally buy the reciever without the relays to save money...just hook em straight up using the pinout on the reciver's page.
The Phidgets part is:
You can even add relays easily to it later if you decide you want to control other parts of your car via the carputer. There seems to be plenty of tutorials on their page describing how to use their parts.
Good luck with it....