I'll try here:
1) There is a folder inside the xlobby folder called client that has the xlobby client for the PPC. Copy the exe and the servers.txt file, just make sure you edit the txt file to point to your XL server.
2)Yes, See above.
3)XL client is more meant for controlling an XL server than streaming.
4) see above
5) I am pretty sure I had to get mine from the Microsoft site. Do you need .net for the PPC client???? I can't remember.
Edit: After reading again, are you sure you understand what XL does? Not trying to be smart I just get the impression you may think it's for streaming music and video, if not just ignore me