How can you stream music through your car stereo with a usb/aux cable itrip fm transmitter with an android?

I have a an android powered samsung mesmerize and i was trying to figure out how to use my itrip car fm transmitter with it because it has a usb port and an auxillary cable . when i plug in the usb to my phone with my phones cable it recognizes the usb but my car stereo doesnt, when i turn to a station thats selected on my transmitter and i try to play music on my phone it doesnt work either. Any suggestions on how to get my music to stream through my stereo?. I have an 02 grand prix gtp