If your OS is Microsoft Windows XP Tablet Edition 2005, and you are running an Intel Duo Core CPU — read up on Microsoft KB Article 922006.

Tablet Edition 2005 has a MASSIVE memory leak in the pen drivers, that will give erratic stylus movement and will affect calibration as well. There is a hotfix available, but you must contact Microsoft directly — as it is not a “public release” yet.

Its an OS issue, not a hardware issue. Microsoft even admits it.

http://support.microsoft.com/kb/922006

The tablet pen recognizer is my biggest pain point, not up to the Toshiba wacom standards.