Excel Re-calculation 2000 compared to 2003

[tonymitchell]

My company has recently deployed MS Office 2003. The previously deployed version was Office 2000.

One of our users has an 11MB financial workbook that contains lots of formula. Mostly of IF, SUMIF and SUM calculations. There are plenty of links between the 25 worksheets within the one workbook but no links to other workbooks.

Entering data into the workbook using Excel 2000 is nearly instantaneous. However entering data into Excel 2003 takes about 15 seconds each time I press enter (or direction key) as the workbook recalculates each time.
The settings for calculation are identical with calculation = automatic.

Any idea how I can achieve the same performance in 2003 that 2000 delivers?
The calculation algorithm in Excel 2002 and 2003 is supposed to better than earlier versions.
I do not want to go to manual calculation as this is seen as a negative step by the user community seeing that they did not need to do that in Excel 2000.

I have confirmed that there are no user defined functions either in this workbook or in my personal.xls file. This workbook also has no macros.