Bluetooth is just a data protocol so it depends what you want to do with it.
The original iPhone can't do the A2DP protocol (this is for stereo audio streaming, or music over bluetooth) so you would need an attachment (i.e. a bluetooth transmitter that plugs into headphone jack). But your car may support simpler bluetooth "headset" functionality (basically to answer calls) and this limited functionality is something I would suspect you could get working.
As for listening to music I would recommend against wireless means as the audio quality is pretty bad. I still like it for the convenience sometimes (I have all sorts of bluetooth audio gadgets) but the music "skips" and stutters every now and then on them all. You can get an FM transmitter and that is also a pretty bad experience in a lot of places (with lots of radio signals).
There are audio receivers (the music player in your car) that have aux in jacks, they basically look like headphone jacks but if yours has that then just getting a male to male 3.5mm cord is all you need. Most other ways are not worth it IMO.