http://download.microsoft.com/download/opticalmouseblue/Install/3.1/MacOS/EN-US/IntelliPoint3.1.OSX.sit

I'm still using this, rather than 5.0, because of the functionaiity it has that disappeared in 5.0 (better control of scroll wheel and buttons). But, it loses some mouse clicks, and I sometimes get a double-click when I actually single-clicked, which is annoying. Don't know what the problem is. Thinking of switching to USB Overdrive, but looks like some users have had some problems with that over the last year, because the developer has been so busy with a new baby that he hasn't had time to release a new update.

Using Mac OS 10.3.6.