I have a powermate as well. I do use it occassionally in FCP. Mostly I use a Nostromo N52 speedpad, which also has a scroll-wheel. I have set that scroll-wheel to zoom in and out (‘cmd +’ and ‘cmd -‘). As a result, I can’t use it to scroll in the browser, etc. So for that I use the powermate.
You have to install the PowerMate preference pane, which you can download from their support page.
Once that’s done, you can assign keystrokes to the powermate’s actions: wheel-left, wheel-right, click; also wheel-left-while-pushed-down, wheel-right-while-pushed-down, and long click.
You could for example assign the arrow keys to the left and right wheel, giving you a jog-wheel function.