Our finance dept have had their machines upgraded from XP Pro and Office
2000 - to Xp Pro and Office XP

Now whenever they open an old (pre-saved) excel sheet - and try to do
calculations on it (like updating data, etc) it takes a age to calculate the
cells...

using an old pc with excel 2000 on then the problem goes away - also copying
and pasting a worksheet into a new one also makes to problem go away (under
Off XP) - but this isnt really a practical way - there must be something
saved in the sheets under 2000 that office XP doesnt like.