That VBA stuff from Lacher will work. However, I would suggest using a template instead.
Set up a blank workbook with the custom header set how you like it. You can also change other things like the default font, custom number formats, whatever. Now you have two choices when you save the file:
1) If you want to ALWAYS use this template for new files, save it as Book.XLT in the XLStart directory. This directory will be under Microsoft Office in the Programs directory. Any time you do File New and select Blank Workbook it will use this template and have your header.
2) If you only want to use it sometimes, then just save it as a normal template file with a name that you can easily recognize, such as CustomHeader.XLT. When you try to save it with an XLT extension, Excel will automatically open up the Templates directory. Then, when you want to open a new file with the header, do a File New and select "On my computer."
To save the template either way, just do a Save As and choose a file type of Template (*.XLT).
I'm assuming that you have Excel 2003. If you use an earlier version, the process will be virtually identical but will vary slightly.