1. Try going to Control Panel - Mouse - Pointer Options - and uncheck "Enhance pointer precision".
2. You might have a virus, here is a link of Joke.MoveMouse virus http://securityresponse.symantec.com/avcenter/venc/data/joke.movemouse.html
3. Magister (aka icon runing away from mouse cursor) virus http://firstname.lastname@example.org
4. Trojan Hiva http://securityresponse.symantec.com/avcenter/venc/data/trojan.hiva.html
Installed XP-Pro and MS Office 2003 on a clean disk, no third party software. From the start w/o a break, the cursor will not stay put while writing. It jumps backward, up a few lines or a page, or disappears. At times, I am typing and nothing appears on the page. No-one has been able to correct the problem which causes great difficulty and mounting frustration.
I've been using PCs since the early '80s and DOS, and never had this problem. Microsoft has no answer.