Something like this should get you going:
Sub InsertNewRows()
Const firstRow = 1 ' change if needed
Const groupSize = 77 ' change if desired
'identify a column where there is
'something in a cell in it in the
'last used row on the sheet
Const baseColumn = "A"
Dim lastRow As Long
'for improved performance
Application.ScreenUpdating = False
'choose starting point
Range(baseColumn & groupSize + firstRow).Select
'initialize lastRow value
lastRow = Range(baseColumn & Rows.Count).End(xlUp).Row
'do the work
Do Until ActiveCell.Row > lastRow
ActiveCell.EntireRow.Insert ' new row
ActiveCell.Offset(groupSize + 1, 0).Activate
'redefine last row
lastRow = Range(baseColumn & Rows.Count).End(xlUp).Row
Loop
End Sub
To put the code into your workbook press [Alt]+[F11] to open the VB Editor.
In there choose Insert | Module and copy and paste the code above into it.
Make any changes to baseColumn and firstRow that need to be made. Close the
VB Editor, choose the sheet with data on it and use Tools | Macro | Macros to
select the macro and [Run] it.
