It is possible by copying (or ftp ing) the relevant files between locations.
Here's what I do for 3 windows PC's (should be the same priciples for xbox though).
1 machine - where I do most of my library updating is designated as the master. From here I upload the relevant files/folders to a share on my server
From this PC I use robocopy to copy the relevant files from PC1 (master) to the shared location e.g.
robocopy "C:\Users\<username>\AppData\Roaming\XBMC\userdata" "S:\XBMC\master_userdata" /MIR /LOG+:"S:\XBMC\master_sync_logs\master_userdata_uploads.txt"
On each of the other PC's I use a robocopy to copy the files from the shared location to PC2 (slave) download the files e.g.
robocopy "S:\XBMC\master_userdata" "C:\Users\<username>\AppData\Roaming\XBMC\userdata" /MIR /LOG+:"S:\XBMC\master_sync_logs\slave_userdata_dowloads.txt"
Note: /MIR does a mirror copy /LOG creates a log for debugging.
XBMC should NOT be running when you do this - while exeryting is alright sometimes I have found that some files can be locked and the robocopy script will sit there retrying the file copies.
You should use the same sources/drive mappings if at all possible - it avoids much hassle.
Do NOT try to merge any files from multiple sources - XBMC always gets in a mess - stick to one machine as the master and you should be OK.
If you want to get more complex you can use profiles and adapt the scripts to manipulate certain profiles only. I use this for adult movies by creatring a profile called XXX (imaginative or what) on the master PC then copying to other PC's - the XXX profile has no 'shared' datrabases just it's own for xxx movies.
The scripts look like this:
robocopy "C:\Users\<username>\AppData\Roaming\XBMC\userdata\profiles\XXX" "S:\XBMC\master_userdata\profiles\XXX" /MIR /LOG+:"S:\XBMC\master_sync_logs\xxx_userdata_uploads.txt"
robocopy "S:\XBMC\master_userdata\profiles\xxx" "C:\Users\<username>\AppData\Roaming\XBMC\userdata\profiles\xxx" /MIR /LOG+:"S:\XBMC\master_sync_logs\xxx_userdata_dowloads.txt"
You can use task scheduler ion windows to do regulalr updates or do it manually. I would think with an XBOX it's just a question of FTP ing the files rather than robobocopy ing them.
Hope this helps
