PHOTOSHOP users NEED YOUR HELP !

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I don't know the problem with photoshop but I can suggest two other programs.

MyPaint is availble for Windows (I use it on Linux) http://mypaint.intilinux.com/ - It is a very good program with layers and layer belnding specifically designed to work with Wacom.

Also, GIMP for Windows http://www.gimp.org/downloads/ - this also works very well with Wacom

I use both of these on Ubuntu Linux but they are both free and open source so you could give them a try

D