How can I map my Bamboo tablet to the entire screen after increasing screen resolution?

The physical drawing area on my Wacom Bamboo MTE-450 pen tablet corresponds perfectly with the edges of the screen when the resolution is 1024x768. However, when I increase it to 1152x864, the tablet is still only mapped to the 1024x768 pixels in the upper left portion of the screen, so the pen reaches the edge of the tablet before the cursor actually reaches the edge of the screen.

How can I utilize the full screen without going back to 1024x768?

I'm running 12.04, 64-bit.