I think that this is usually a bad idea. It can mess up filters, graphs,
pivottables, ...
If you want to make it look double spaced, then increase the rowheight.
But you can do it a few ways.
One way (manual):
Insert a new helper column
put =row() in the top cell of that new column and drag down (>400 rows)
Then convert those formulas to values (edit|copy, edit|paste special|values)
Then copy those numbers to the rows directly beneath the >400 rows.
Now select the whole range (row 1 to > row 800).
Sort your data by that column.
Delete the helper column.
Another way is to use a macro.
This picks out a column that has data in it on the last row -- I used column A.
Option Explicit
Sub testme()
Dim LastRow As Long
Dim FirstRow As Long
Dim iRow As Long
With ActiveSheet
FirstRow = 2
LastRow = .Cells(.Rows.Count, "A").End(xlUp).Row
For iRow = LastRow To FirstRow Step -1
'to increase the rowheight to twice the height
'.Rows(iRow).RowHeight = 2 * .Rows(iRow).RowHeight
'to insert a new row
.Rows(iRow).Insert
Next iRow
End With
End Sub
If you're new to macros, you may want to read David McRitchie's intro at:
http://www.mvps.org/dmcritchie/excel/getstarted.htm