Printers disappearing and reappearing.

Hi folks,
A person in my office has been having issues with her
installed network printers. She uses Win 2000
Professional, and over the past few weeks has suddenly had
her installed printers "disappear" (i.e. there is nothing
in the Installed Printers view) and thus no applications
can find printers to print from. If she reboots the PC,
the printers show up again normally and she can print
without troubles, but we were just looking for some
insight into what might be going on.
I know that this same problem occurs in Windows NT fairly
often, and it sure seems that you can use the same method
to fix it...but what can I tell her is going on?
Thanks.