as far as i remeber, for a wacom that is, that is done in the tablet propertes?

i just looked and there is a number of differant things i can change, right click, left click, modifier?? but no opacity so i guess it would be done in photoshop, (anything can be done in photoshop, its as big as maya) you would have to look at the help menu i think, looks like no-one knows for sure.