if you learn more about it, then come back with an attempt at a schematic im sure we could help you finish it.
some things to google might be, microprocessor, junebug, pickit2, avr, bluetooth module, bluetooth ssp for a start
you'll need a microprocessor of some kind, a bluetooth module, some relays, trransistors etc. if your not experienced this may be too big a project to start with, but if you convince me that your serious, by doing the leg work, then i'll help you out, as im sure loads of others on here will.
do you intend to use a mobile/pda/computer or some other kind of device to talk to the car?