Insert New Rows Between Rows

Hey guys,
I found out that selecting multiple rows by hand and then inserting rows would result in inserting new rows between the selected rows.
The following macro shows this:

[VBA]Sub Macro1()
Range("1:1,2:2,3:3").Select
Selection.Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
End Sub[/VBA]

Now, what I need to do is this:

[VBA]Sub test()
'Getting the last Row
Cells(1, 1).Select
lastRow = Selection.End(xlDown).Row
'Building the Selection
For i = 1 To lastRow
selectionString = selectionString & i & ":" & i & ","
Next i
'Removing the last ","
selectionString = Mid(selectionString, 1, Len(selectionString) - 1)
Range(selectionString).Select
Selection.Insert Shift:=xlDown, CopyOrigin:=xlFormatFromLeftOrAbove
End Sub
[/VBA]
This is trying to select each row individually to insert rows between the selected rows. As expected, I get the following error as it tries to select the rows:

Run-time error '1004':

Method 'Range' of object 'Global_' failed

I know there are plenty of ways to achieve the same result by creating a simple for-loop and inserting a new row after each row.
This is NOT what I want to do, since this seems to be a lot slower. (I am speaking about 200.000-300.000 rows)
Any ideas no how to get this working without a loop?

See if this is any good for you. You highlight the rows you want to copy and insert then enter how many times.

[vba]
Sub CopyAndInsertRow()
Dim NextRow As Long
Dim NrOfCopies As Long
Dim i As Long

Const NrOfCopiesDefault = 1
Const NrOfCopiesMaximum = 9

Do

On Error Resume Next
NrOfCopies = Application.InputBox(prompt:="How Many Copies Do You Want To Copy & Insert?", _
Title:="# COPIES", Default:=NrOfCopiesDefault, Type:=1)
On Error GoTo 0

If NrOfCopies = 0 Then
MsgBox "No copies made.", vbInformation, "CANCELLED"
Exit Sub
ElseIf NrOfCopies > NrOfCopiesMaximum Then MsgBox "Please Enter Number Of Copies Between 1 and " & NrOfCopiesMaximum, 48, "ERROR"
End If

Loop While NrOfCopies < 1 Or NrOfCopies > NrOfCopiesMaximum

With Selection
NextRow = .Row + .Rows.Count
Rows(NextRow & ":" & NextRow + .Rows.Count * (NrOfCopies) - 1).Insert Shift:=xlDown
.EntireRow.Copy Rows(NextRow & ":" & NextRow + .Rows.Count * (NrOfCopies) - 1)
.Resize(.Rows.Count * (NrOfCopies + 1)).Sort Key1:=.Cells(1, 1)
End With

End Sub
[/vba]

Pretty neat solution. I'll give it a try :)
Thanks