One of the frustrations of using Basilisk II under OS X is the barebones GUI for setting preferences. It works well enough for most options, but it doesn't make it easy to select and manage disk image files. (I'm referring to the ports of the main development line of Basilisk II, not Nigel Pearson's port which includes its own OS X-style Preferences menu.)
I've wasted some enjoyable time writing an Applescript that makes it easy to select and manage the disk images listed in .basilisk_ii_prefs. It lets you add and remove images, set a different image at the top of the list to become the startup drive, create new images and add them to the list in the preference file, and set the option to boot from a CD-ROM.
It should also work with SheepShaver by changing a single variable at the top of the script, but I haven't tested it with SheepShaver.
It's obviously the work of a beginner at Applescript, and an expert coder could probably reduce its size by two-thirds, but it seems to work. Run at your own risk, and please feel free to let me know of any problems. Download it here if you're interested:http://www.columbia.edu/~em36/EmulatorDiskImageChooser.zip
Edit: Slightly improved version (better error handling) posted 20 August 2009.