A couple of items to take note of, be sure and read both announcements:

Standalone Beta Patch We have become aware of a bug in our patching system that would have prevented future patches of the beta client from being delivered properly to all of our beta testers. In order to fix this, we need all beta testers to download a standalone patch. This patch will also allow us to test our standalone patching capabilities of the World of Warcraft beta client in case future updates need to be made via multiple methods, i.e. through the Blizzard Downloader, mirrored patch files, or by any alternate delivery systems. Please make sure you have at least 3 GB of free space before you run this patch. For details on what balance changes have been made, please read the patch notes here. To download the patch, PC users go here and Mac users go here. If you have difficulty installing the patch, please unzip the patch file to the same directory in which you have World of Warcraft installed and run it from there. PC users should have the patch file "WoW-0.9.1.exe." Mac users should have the file "WoW Mac 0.9.1 patch.dmg." If you experience difficulty installing the patch, please contact wowtech@blizzard.com.

And

Standalone Beta Patch Update We have identified a bug with the standalone beta patch that beta testers with fewer than 3 gigabytes of free space on their hard drives encountered when attempting to install the patch. Please see the Technical Support forum post here that describes the solution.