The updates, which weigh in at 64 and 36 megabytes respectively, require Mac OS X 10.5.8 (Leopard) or 10.6.1 (Snow Leopard) in order to install. Alternatively, yet to be released OS X version 10.6.2 is slated to have native Magic Mouse support and will not require this update for the multi-touch functions to work.
The Magic Mouse is included with the newly introduced iMac models. The standalone version of the mouse retails for $69.
The Magic Mouse is the world's first multi-touch enabled mouse and was introduced October 20th alongside updated iMac and MacBook models. It replaced the Mighty Mouse, which had to be renamed the Apple Mouse due to trademark issues.