Though it doesn’t say it in the description the FeedBurner FeedSmith plug-in it does work on WordPress Network (Multisite) installations (WordPress 3.0X).
for the details on the installation. Where it says “Activate” then instead just click “Network Activate” and the plugin will be available for all the sub-sites.
Within each site the Settings -> FeedBurner settings will be unique to that site.
What the plugin does is redirect the normal /feed path to the FeedBurner page that you have previously setup and have configured in the plug-in settings.