Instead of hiding the rows, maybe just using data|Table would be a better way to
allow the users to input data.
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But if you want to hide the rows, I think hiding them when the workbook is
opened will be an easier design.
If you hide them when the workbook is saved, it might irritate the current user
if he/she still needs to see that data.
If you hide them when the workbook is closed, then you'll have to save that
workbook. And if the user made a massive error and wanted to close without
saving, you may be saving that massive error.
I'd use a macro that hides the rows when the workbook is opened:
Option Explicit
Sub Auto_Open()
With Worksheets("sheet9999")
.Select 'make it the active sheet
.Range("a2", .Cells(.Rows.Count, "A").End(xlUp)).EntireRow.Hidden = True
End With
End Sub
This goes in a General Module--not behind a worksheet and not behind
ThisWorkbook.
If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm