Just as an FYI, I had not used Mocha AE since I upgraded to Snow Leopard and it turns out there is a bug where Mocha AE (the version included with after effects) will not display video. To overcome this, output your sequence as a PNG sequence and load that into Mocha to use for setting up your tracking. The Mocha folks have not stated that they intend to fix this issue. They are currently telling folks to upgrade to the full version.