Excel 2007 slow opening files from the network

We recently updated a number of users who had been using Office 2000 to
Office 2007. It is asazing how slow Offie 2007 is. We timed opening a 7MB
file in a remote office in Excel 2000 three times and it was consistently
running at about 5 miutes. When we tested Office 2007 on the same PC it was
between 45 and 50 minutes. That is awful. Is there some tweak we can make so
that I can keep Office on these PC's?

All the PC's in question are running XP SP3 and have decent if not
spectacular hardware. The problem exists on brand new PC's as well as the
old.
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Bettie