I defined a few functions in a workbook using VBA, and then expected to be able to use them in a cell formula - but Excel does not recognise the function. I just get #NAME?<
If you are using the latest versions of Excel, to see VBA functions in another workbook you need to:
Save your workbooks as .xlsm
Enable macros as suggested above
Set a reference. In VBA (Alt-F11) choose Tools/References, then browse to the workbook which contains the macro you want to use. Check that reference in the list.
If you get an error message about the module names clashing just rename it in the project explorer first.