Wacom intuos 2
Which century was that? May be a simple compatibility issue - PS has evolved, the Wacom tablets and their drivers as PS uses them have evolved. Short of playing with different drivers and settings, I doubt you will ever get it to work reliably...
Mylenium might be correct on the Wacom driver, and PS CS 6 (if you have not installed the latest driver from Wacom, I would do that), but to check things out, I would Reset the Brush Tool's Options. Next, I would verify that I had created a New Layer (a "regular Layer," and not, say a Shapes Layer), then check that I had no Selections active in that regular Layer. Those can be common reasons why some Tools do not function, as they should.
I also have an Intuos 2, but have not hooked that up to my PS CS 6, so cannot directly comment on the drivers for it, with CS 6. Maybe I will have time to install the drivers, and hook that up to my laptop next week. Will report on how it works for me.
Thanks for the advice and trial-n-error guys, I'll make sure my drivers are updated for the intuos 2, and in the meantime try to isolate the problem further. I'm definitely keeping layer-mode on normal and regular.