Wacom Intuos5 Pen Pressure won't work

I just got the Intuos5 and it works well except for the pen pressure feature for varying brush size or opacity. I can't get either to work. I have the latest driver, I think (where is the driver located on the Mac in OSX 10.6.8?). The tablet is attached directly to my iMac. I've sent two message to Wacom tech support and they don't respond. Any idea as to how I can get this working?

Thanks,

Fran