Windows XP Professional, Excel 2003, 2GB RAM

When our heavy Excel user has five or more instances of Excel open, usually,
the display begins to fail. It's as if each sheet were composed of tiles and
the tiles were randomly moved around. Also, the programs no longer respond to
mouse clicks or keystrokes.

I disabled all graphic features to no avail; no entries in the Event logs.

Thanks for any help.

Tom Morris