What transmitter should i use?

I have the new Droid X phone by Verizon and i put music on it. now i dont have an ipod so i bout a transmitter to use in my truck cause i hate when there aint good music on the radio. i bought a transmittter and it says on my phone that it doesnt accpet it...is there a certain transmitter i should use so i can play music through my truck speakers from the phone or is this a lost cause?