I assume this is the same for iTunes purchases. I have the same problem when trying to share iTunes purchased songs from my iPod to another computer. The workaround has been like you said.. burn a copy to CD and then rip to MP3. The corresponding MP3 should play on the Treo. That being said, Apple is working with Motorola to bring iTunes to their next generation mobile phones. I'd like to see PalmOne work with Apple on this since the Treo has removable media...it can store a decent amount of music. Here's the
link to the press release