Surely, this is the final nail in ROKR's coffin. Tea Vui Huang has created a "Windows-based iTunes Add-on for Sony Ericsson Walkman Phones, Sony Clie PDA and Sony Ericsson P900/P910 Smartphone"—it's called the Mass Storage Synchronizer. Here's the gist: MSS makes Sony devices show up as a folder in iTunes, and then through some crafty app-synchronization the software copies the contents of the folder onto the Memory Stick in the phone or Clie. This doesn't look like the simplest of processes, and there is probably a manual way to do the same thing. I don't have the time (or the phone) to test it out. But Huang has created some interesting Podcasting apps in the past, so this is probably worth a try.
Mass Storage Synchronizer [Product Page]