Time machine is a new feature in Leopard that backs up your data but by default it only supports backing up to another physically attached hard drive.  There is however a work around to get it to backup to network shares;

  • Go into Applications / Utilities and open terminal
  • Type in defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1 and then press enter
  • Mount the network share (cmd + k)
  • Go to System Preferences, open Time Machine and select change disk
  • Then select the share that you want to backup to and Time Machine should then backup to it