I dont know about remote desktopping to a Mac machine. But, you can use remote desktop to connect to a Windows XP box from a Mac. I actually use it frequently.
You can download a free copy of Remote Desktop for Macs from Microsoft website, I believe. Unfortunately, I dont have a link for you. Just do what I did which was a google for the following key words. "Remote desktop Mac"
Think this is more designed for support that simple file sharing which I require.
I will wait till the powerbooks are updated (say, October / November time) and buy then. It will probably be the last PowerPC powerbook. How do you think they will update the next powerbooks? (A little off subject here - sorry)
Then I ignore that comment (go to the Rumors forum for that) ... Microsoft's RDC (free) solves your problem, obviously, and can also be used for file transfer. But if you only need file transfer, it'd probably be easier to actually network the two computers using Windows SMB file sharing or activating FTP on the PowerBook... Remote Desktop uses much too much resources for simple file transfer.