I have made a mp3 player some years ago, that works on the cd changer interface of my car radio. There is a Atmel AVR inside that reads a hdd in PIO mode forwarding data to an mp3 decoder chip and doing the radio interface job.

Now it would be nice to have WLAN access to the mp3 files in the car, because usually I do not take the hdd out of the car and when I want to have a new song on it I don't want to go outside in the cold to get the hdd.

For this reason I have bought a WL-HDD. Now I have to customize the firmware. The easiest way I can imagine is to modify my player to be a USB serial device. I could send commands from the car radio via USB to the WL-HDD and then receive the mp3 file data via USB from the WL-HDD.

Now I know how to program an Atmel AVR with the gcc compiler and some command line programs with bloodshed, but I have never compiled anything with linux inside.

What development environment is needed? Do I need linux running on a PC for the development environment? If yes, what linux? Can I do it with Knoppix or Kubuntu?

Please help me getting started.