It finally worked. Thx to everyone for the help, direction and inspiration to understand how VBA works. Now I know a little bit more. This ended up being my solution:
Private Sub OpretSerieNrKnap_Click()
If [Forms]![OpretSerieNr]![Basic500Amount] > 0 Then
Dim count As Integer
For count = 1 To [Forms]![OpretSerieNr]![Basic500Amount]
Dim SQLbasic500 As String
SQLbasic500 = " INSERT INTO SerieNr_Label ( Varenavn ) " & _
"SELECT 'Basic500'"
DoCmd.RunSQL SQLbasic500
Next count
End If