I'd recommend making sure that you have the latest tablet drivers installed first. Download them from www.wacom.com, uninstall your current tablet drivers, restart your computer then double click the downloaded file to install the latest drivers. A lot of problems we see with tablet input are solved by updating to the latest tablet software version like this.
If this doesn't help, please let us know which version of ArtRage you're using and what operating system you're using it on so we can give you some more specific troubleshooting steps. ArtRage normally works out of the box with these tablets as standard, but we may need to change some input settings depending on your configuration if you're getting odd behavior. Also can you let me know whether you are getting this behavior for all tools in ArtRage or some specific tools.
Resident Bug-Hunter and Support Guy