Stop auto recalulation of older spreadsheet versions

[Harry]

Using excel 2000 (sp3)

I have to use spreadsheets saved in excel 97 format - every time I go to
close them, even though I've made no changes I keep getting a prompt to -

"Do you want to save the changes to xxx.xls"
"MS Excel recalculates formulas when opening files saved in older version
of excel"

Can't find any option to supress this - is it possible or is it yet another
of MS's forced upgrades?

thanks

harry