I have a template workbook (Excel 2003) that the user enters data in. When
finished the user should press a button and the script should look in a
specific folder:

c:\datafolder

The folder contains a list of files:

A0001.xls
A0002.xls
A0003.xls

The script should now save the file with the next "available" file name:
A0004.xls and enter the file name in cell A1.

Can anyone help me out?
The Doctor