I recommend creating some custom rsync scripts/batch files. I've written similar things mostly for my work laptop and desktop so I can just sync all changes so that both machines have the same up to date information.

The logic of my script goes something like:
1)Sync changes from Desktop to Laptop
2)Sync changes from Laptop to Desktop

That way if I change one file on the desktop, and a different file on the laptop, then after the sync, both boxes have the updated files from each other. The only downfall to using that method is it doesn't handle file deletes or editing the same file on both machines. So if you delete a file/directory on one system, then the next time you sync you would re-sync the deleted file/directory. And if you edit the same file on both machines then I will end up with the file that I edited last.

The other catch is that you'd have to install an rsync server/client on the windows machines, something like DeltaCopy etc.. Or perhaps the cygwin version of rsync (which could support using rsync via ssh)

All of that stuff would have to thrown in a script or batch file. For your implementation I would sync in this way:
1) Sync from Media Server to File server
2) Sync from Gaming Laptop to File server
3) Sync from Ubuntu laptop (the *nix versions of the rsync clients support using rsync via ssh, which IMO would be a better way of doing it, otherwise setup rsyncd and make sure the port on your ubuntu firewall is opened up if you have one.)
At this point your File server should have all latest version of the files:
4) Sync from File server to Media Server
5) Sync from File server to Gaming laptop
6) Sync from File server to Ubuntu laptop
Now all of your machines should be up to date
7) Backup using the File server to Mozy.

This implementation also doesn't take into account if you make different changes to the same file on multiple machines... that would get nasty, again, this solution in that scenario would result in having the version of that file that was modified last.

Hope that helps... there might be a much more elegant software solution out there but if you want to do it yourself, I would do what I described in a little sync script/batch file. I can't stand the CLI in Windows so would prefer doing it on a Linux server, but if that isn't an option then I use cygwin.

Sorry for the rambling....I'm done now...