Printer Problem

Hi all
My daughter has a P1 Toshiba laptop that she uses for Uni purely as a word
processor.
It's running Win98 and has a monochrome HP 400 series printer attached and
access to the net via a network card to a router.
The problem is that she can use the PC for hours on end with no problems
whatsoever but whenever she prints some work the thing goes haywire.
Windows open at random, the taskbar moves itself and the mouse pointer
cavorts all over the screen.
The problem happens AFTER she has printed and the print jobs are fine, no
matter how many pages are involved.
I re-installed the HP drivers to no avail and the only solution is to
re-boot the machine after which it again runs perfectly - until she has to
print again!!
Any ideas?
Neil.