AirTunes is an encrypted format. Anyone attempting to break the encryption in the USA will be doing so in direct violation of the DMCA. I don't like it, but there it is.
Oh... and it is Apple's lossless codec inside that encryption, so it is unlikely that a Palm would be up to the task of decoding it real time. The AirportExpress can only handle it because it has well tuned codecs running on specialized hardware.