Number down in a free column 1-500 behind the data and then do it again
in the same column below the data(so you have 1-500 twice) Now sort on
that column.

Quickly could be a macro but see NOTE below macro.

Sub InsertALTrows()
'David McRitchie,  misc  2001-06-30
   Application.ScreenUpdating = False
   Application.Calculation = xlCalculationManual
   Dim i As Integer
   For i = Selection(Selection.Count).Row To Selection(1).Row + 1 Step -1
       Rows(i).EntireRow.Insert
    Next i
   Application.Calculation = xlCalculationAutomatic
   Application.ScreenUpdating = True
End Sub

Select A1:A500 using namebox then run the macro.

NOTE:   I would not recommend doing this if just for appearance sake.

Set the rows to double height instead.

The blank rows can mess with filtering, copying, sorting.

Gord Dibben  MS Excel MVP

The 'ghetto' way i learned to do this back in the day is in the last column
name cell x1 something, enter 1 one in x2 and a 2 in x3, hightlight both and
copy down, you should now have your data numbered 1-500, select that column
from 1-500, copy it, and paste it after 500 so you now have 2 sets of 1 to
500. Sort by that column and you're done, pasteone time for every blank you
want.

Do you really  need the extra rows?

Maybe selecting the range (rows 1:500) and changing the row height (double it)
would be sufficient????