I want to set up a standard header that can be used on multiple sheets, and I
need it to look the same on sheets with different column widths, different
row counts and even different scales. I basically need Excel to treat the
header separately from the content so all the worksheets have a uniform feel,
the way powerpoint contents sit on top of a uniform background that doesn't
change even if the contents vary widely from slide to slide.

I know how to get text into the header, but I need a solid horizontal line
under the header all the way across the top of the page (except for perhaps a
1/4-inch border on either side) that separates the header from the contents
in the main body of the worksheet. MS Word handles the horizontal line nicely
with "page borders" but I can't seem to find a comparable feature in Excel.
Is there such a feature, or at least a good workaround?