I just checked it out myself! It looks like it is just a charger! Most have to plug into the head phone part to transmit music to your radio!
Heres what one should look like:
Car FM TRANSMITTER for ZEN/IPOD/NANO/Sansa/Zune/CD/MP3 - eBay (item 370065757844 end time Jul-05-08 18:51:38 PDT)
I hope this helps!