Firmware for car stereo

ok so this might sound strange but I am totally new to linux but have some background in programming but not too much. I am confident I can figure it out but I need a user friendly tool to play with. My overall goal is to attempt to replace the firmware with a bootable hard drive on a car stereo dvd player with monitor. So I want to start playing with linux and see what I can and can't do and go from there to eventually maybe create an os or maybe just use an existing linux based os and have a program with an interface that automatically boots up when the the os does. So anyone that can help with a good tool to start and practice as well as anyone forseen problems I might have and solutions. It's a huge challenge for me but I'm hoping if I do the research and a little friendly help I can accomplish it.

THANKS