This is from the January 24, 2005 program of Fresh Air with Terry Gross.
It's pretty cool. Colbert discusses his ideology and protocol for comedy. Specifically, what he considers fair comedy, and what kinds of comedy aren't allowed. He has rules. Neat interview. Check it out.
Stephen Colbert On Fresh Air - Part 1 of 2 (MP3 - 26 MB)
Stephen Colbert On Fresh Air - Part 2 of 2 (MP3 - 22 MB)