on M$ RDP client, basic file transfer can be achieved by enabling 'local devices' in the 'resource sharing' tab of the RDP connection. The local drives (from your RDP client machine) are then exposed as mapped drives on the target machine.

I therefore assumed that checking one or more of the "Disk Sharing" check boxes on the front end connection details screen for rDesktop would work the same way ... but I just tried it & it didn't - checing myDocs and/or Mem Card's seemed to have no effect on the target PC. Not sure if that's a bug or if I'm just misunderstanding the purpose of those check boxes. I'd be interested to know the answer either way ...

nb - Only contemplate this method (even if it works) if you trust the target system to be secure and virus free; it potentially exposes your n900 security-wise.