The MP3 of the radio interview with Amitav Ghosh is here, at the wonderful Internet Archive.
I would also recommend the conversation on the same program the following night, with Professor Kim Scheppele, on putting the recent referenda on the EU Constitution in perspective. She's worked with the Afghanis as a consultant on their constitution, and is going to be working with the Iraqis this summer during their Constitutional Assembly.
You can also find all of the other downloadable episodes of Radio Open Source that have made it through the Internet Archive's cue by doing a search for "Christopher Lydon" at their site. Thus far it looks like 5 episodes of the show in all are available. (Incidentally, their search engine is a little screwy; you get different results if you run the search multiple times!)