I also have had some problem using Mouseworks 3.0 and Kensington Mice (various models) under Mac OS 10.4.6 and 10.6.7. In a recent exchange (earlier this week) of support message with Kensington their rep indicated, and I quote:
"We are sorry to inform you that the feature to zoom with the scroll wheel is disabled on Mac OS. We regret to inform you that the feature is not available in MouseWorks as well. Be advised, we would like to inform you that the MouseWorks is not compatible with your operation system."
I wrote back that, in fact, it does work on my Mac, except for the Universal Access Zoom with Scroll Wheel feature. I also asked if the plan on upgrading Mouseworks. This was their second answer:
"
Thank you for contacting Kensington Technical Support.
We apologize for the inconvenience caused. We regret to inform you that Kensington has no plans to update MouseWorks for Mac OS 10.6 and no other drivers are compatible to program the scroll wheel to zoom.
We apologize for any inconvenience this may have caused to you."
My solution - Junk Kensington and go buy a Microsoft (for Mac). or Logitech. They both work fine on all our Macs (we have four of them) and are fully programmable with those other drivers (as long as you buy the right models)