Vista Tutorial - pointer and cursor instability

Pointer instability seems to be associated with some activity of the
operating system. but I was not able to find what activity. In general by
reducing a load situation improved, but the problem persists.
The cuursor jumping is another problem. It jumps not randomly, but to the
pointer position. When tapping is disabeled the situation improves. The other
trick is to position the pointer somewhere, so not to disturb typing
sequence.
In another machine running XT, the pointer instability appeared in
connection with traasparency scanner, apparently the scanner driver problem,
and it appears after 1-2 scans.