After Yahoo has launch Yahoo Messenger 10 Beta (for Windows user including Windows 7), right now Yahoo also launched for Mac users (Apple): Yahoo Messenger 3.0 Beta for Mac. Unlike in Windows Edition that you usually face online installer, the Yahoo Messenger 3.0 Beta can be found easily the offline installer aka stand alone installer for the official download page of YM 3.0 beta for mac.
This beta version would be more stable that the older version, especially when works under new Mac Operating System: OS X Snow Leopard.
Features available in Yahoo Messenger for Mac 3.0 Beta
The features including Yahoo Insider, Local News, Access to Weather, Mail
Inbox, and Search Engine faster, and much more (including bug issued fixing).
Download and Install Yahoo Messenger 3.0 Beta for Mac
First you can download the installation package (dmg file) here: Download Yahoo Messenger 3.0 Beta for Mac, then double click the download file to begin the installation.