LEDs - underbody kits, cathodes, flexible LED strips, dome lights
They have hardware that can handle what you want. Also, if you must do tubes, I'd recommend CCFL (cold cathodes) or LED tubes. Personally, I use the LED strips in my vehicle, as I find them easier to hide (I can't STAND seeing the source of the light). Look for the music interface... that will give you your desired light response. As for just using the illumination at night, a simple rocker switch will do.... when you run your +12v to the lights, simply put a switch somewhere convenient for you... presto, you're done. That site also has some ok forums, so I'm sure any other questions concerning vehicular illumination can be handled there as well.
