The Storm would need FM Transmitter circuits installed as part of the base hardware. From the pictures I have seen of a disassembled Storm and the documentation about what each part was, there is no FM Transmitter just like there is no WiFi for the 9530. It would be hard for a BB Developer to write an application for hardware that does not exist.
There are several BB programs that will allow you to stream FM channels to your BB. I believe Slacker.com will be releasing a version of this for the Storm shortly. However, this is not what you were asking for.
What may satisfy your request is for a hardware vendor to create a BlueTooth FM transmitter that the BB could pair with. This would then allow you to stream your music to your car radio. I have no idea if something like that is available or in the works but a search through Google might turn something up.