UDFs Recalculating And Changing Cells

I have been asked to look at moving a very large set of pricing sheets from Excel 2000 to Excel 2003. In the progress of this I have found that the functionality for a UDF in a cell to change/recalculate any other cells has been removed in Excel XP, whereas it was available in Excel 2000. The amount of work required to refactor the code is very large, and before starting on it it would be good to find out if there is a workaround.

The Sheet works in the following way:-User enters values, clicks a button to run a Macro,-Macro calculates all the ranges required to return a price-In many of the cells it is calculating are Functions which go and look at a large number of cells to calculate the price, sometimes writing to other Cells and sometimes having to recalculate other cells-As it is such a large sheet we can't simply calculate all cells before we tell it to price, as they are not all needed and so aren't calculated unless needed for performance reasons.It would be a lot of work to move the functionality from the Functions to the initial macro call, though this would solve the problem. Is there any other workaround?Macro security is set to low.The Errors I receive are the following:The UDF will hit a line like Range("DataRange").Calculate and this will raise a "Calculate method of Range class Failed" error. If it hits a line like Range("DataRange").Value = 1 this will raise a "Application-defined or object-defined error"If it hits a line like ActiveWorkbook.Names.Add Name:="This_Name", RefersToR1C1:="=Sheet1!R8C2" then it also raise a "Application-defined or object-defined error".Any of these run from a UDF in Excel 2000 works.I have a sample workbook if this isn't clear