You should be able to use a workbook created in 2003 in 2000 with
little or no modification. There are few functional differences
between the two versions and the file format is unchanged and the
object model is unchanged with the exception of the new features added
in 2003.
What problems do you encounter when attempting to use the 2003 xla in
2000? As a general rule, you should always develop for the earliest
version that you need to support.
Cordially,
Chip Pearson
Microsoft MVP
Excel 1998 - 2010
Pearson Software Consulting, LLC
www.cpearson.com
[email on web site]