Use StuffIt Expander to unzip this file. Use your browser to upload the 'code.bin' file from your Linksys setup page: http://192.168.1.1/Upgrade.htm
If that doesn't work for you then you can use MacTFTP to install the firmware update. For step-by-step installation instructions using MacTFTP, read here:
What's new in this version:
- Fixed xml authentication bypass issue.
- Fixed UPnP buffer Overflow issue.
- Fixed password change without authentication.