that is only a shortcut and cant be used while painting.
Are you saying the shortcut doesn't work at all for you or how does it seem different from say photoshop 7?
What operating system?
I'm using Windows 7 here at work. I recall being able to use shift and the keypad to control flow in Photoshop 7. A co-worker showed me that the feature is working in CS5 with the number keys but not while useing the keypad... Hopefully someone knows of a fix or some more information at the least.
Are you left handed? Just wondering why you would be using the keypad, and guessing you might have pen or mouse in your left hand. If that is the case, then I think you are out of luck, because it only seems to work with the number keys on the main keyboard.