I got a new system, and in trying to get the Radeon HD 5450 to output to 3 monitors at once, I booted to an old install of Linux Mint. After updating, and far too much fiddling with drivers and kernels, and rebooting, I got it to work, albeit not consistently. I decided to switch to Mint from Ubuntu on my main install, hoping that I would have better luck with a fresh install than I did with an incorrectly updated system.
This is a short how-to for restricting a drawing tablet (also known as a graphics tablet) to a single screen. When you have 2, 3, or 4 (or more) monitors, input devices might not work exactly how you want them to because of the difference between desktop size and monitor size (when using big desktop or xinerama. As an example, I have 2x22" monitors, each capable of displaying 1680x1050. My desktop size is therefore 3360x1080, and that is what my tablet maps to.
I'm using an older computer to do real work (I don't game) so I've chosen to forego the fancy desktops and stick with XFCE4. It is a bit lighter than the tricked out desktops, and using it doesn't require that I adapt to a new paradigm.