iTunes does not like to sync with anything other than an iPod, or an Apple device. Download and install the Audible Manager for OSx and use it to authorize your Clip Zip for Audible content.
Drag and drop cannot be used, as the license data is missing. There is anAudible Manager version for OSx here.
It’s also critical that you install the SanDisk Digital Players Plugin once you have the manager running. To do this, open the Manager, click on Help > Check For Updates, and select the Sandisk plugin. Next, plug in your Clip Zip. You can then authorize your Clip Zip and transfer your books!
SInce you are using a platform that is hell-bent on using iTunes (it was designed that way, of course), the Achilles’ Heel of using the Clip Zip, or anything other that an iPod, is iTunes itself, as it doesn’t show other devices as available for synchronization / transfer. Simply use the Audible Manager in your case. For the Audible Format, use Format 4 or Enhanced with the Sansa, as these are the supported formats. I am happy with Format 4, though it is a little larger than the lower formats. (Format 4 offers great sound quality-the 1-3 formats are not compatible with the latest generation Sansas.)
The Manager will be needed for download and transfer using your combination, since you cannot use the alternative, Windows Media Player. The Manager is a good client, allowing you to follow your book progress while the device is connected and charging, a nice additional feature- as well as multiple bookmarks when listening on the PC or Mac.