This is a known behaviour. For tablet pc's there is a special hook for the display which is executed whenever the mouse is moved. The thread for this hook has lower priority then normal, causing the mouse pointer to be jerky. So this occurs on every tablet pc (I have a Toshiba Tecra M4, having the same issue).

Please see http://support.microsoft.com/kb/900475/en-us. Hopefully, Microsoft will release the patch in July or August 2006.