That's an odd one! Have you tried enabling "mouse mode" under the Edit, Preferences menu then restarting ArtRage? Vista by default will tend to use ink services but using the mouse mode method ( that was going to get silly with any more Ms ) for getting tablet points would work around any potential issues with that.
You'd also find that if you weren't to use Mouse Mode, tilt would not work, as I don't believe that Ink services support that.
Feel free to email me at firstname.lastname@example.org if that doesn't help. I'd be glad to work through it with you and see what we can find out.