sound activated interior lights?

I think this is a job for DealExtreme

Have a look through their LED Car Deco. A quick looksee revealed this:
DealExtreme: $8.99 Music Activated Dancing Light Bars for Cars
DealExtreme: $10.83 Sound Controlled Music Light for Vehicles (2 Lights)

 

You can get CCFL for computer desktop case. You can get one for $5-$10. You can get them from local PC stores or even Radio Shack. They run on 12V and even come with sound activation.

I used to have it in my previous car. Since it is not designed for cars, use it only for the interior.