Resolution:
The problem appeared to be the default printer (Brother HL1435). When I
changed the default printer to a network printer, the problem disappeared.
So I completely removed all traces of the HL1435 and re-installed it from
scratch. It is now the defualt printer and the Print Preview is functioning
normally.

Most of our office systems have Excel 2000 with Window XP pro SP2 and they
operate without any problems. The most recently installed system (Dell
Dimension 3000) has an issue with the Print Preview. When you first open
Print Preview, all the buttons are active and clickable. After about 10
seconds, the "Print", "Setup" and "Margins" buttons go gray and can no
longer be used. This system has a default laser printer attached to LPT1
(like some of our other systems). I have re-installed Office with no change
to this behavior. Any ideas?

TIA
Sue