You will need the appscript package for the fancy disk image creation to work:
sudo easy_install appscript
For Snow Leopard (which uses Python 2.6), you will need the param_parser package:
sudo easy_install argparse
This script should not be run manually, instead, after building as usual:
make deploy
During the process, the disk image window will pop up briefly where the fancy settings are applied. This is normal, please do not interfere.
When finished, it will produce Bitcoin-Qt.dmg.