req: PSU for avr project in an auto

[chrometsuba]

I'm looking to move a dataloging project from my desk to my car to start doing real-world testing.

The unit reads inputs and processes the data on an atmega128 cpu, displays data on 7 segment LED displays and handles user data.  I haven't checked my actual power usage, but it shouldn't be anything out of the ordinary (100-500ma?) 

My main concern is isolating the unit from the other electronics in the car, such as a ham radio and the cars ECU/ignition system. 

Anyone have any schematics floating around that will fit the bill?

thanks