The firmware is at the firmware upgrade sticky at the top of the forum, under each of the “All Regions-Click here to download” links. http://forums.sandisk.com/sansa/board/message?board.id=clip&thread.id=15109 Select the firmware applicable to your Clip, according to the directions.
The Clip should be set to MSC mode for a Mac. It might work to do a Clip system reset (with the Clip off, hold the on switch uppermost for 15-20 seconds) and then try again (again, with the USB Mode set to MSC first).