He's already paid for over 400 songs. Why should he have to pay for them all again? I know I wouldn't.

Unfortunately, it seems all of the music services do this, so I think you're out of luck, William. iTunes will usually convert files from other formats unless they're embedded with some sort of digital signature (Sony does this, and it's very annoying), but it doesn't sound like you want to use their service. You might consider trading the Ipod in for something that's more Napster-friendly. It's really a shame that the services work this way, but that's business for you!