Here's something I posted a while back in response to a similar question ...
You can do it with some code in the Page event procedure of the report ...
Private Sub Report_Page()
Dim sngTop As Single, sngLeft As Single
Dim sngWidth As Single, sngHeight As Single
Me.ScaleMode = 3
sngTop = Me.ScaleTop + 5
sngLeft = Me.ScaleLeft + 5
sngWidth = Me.ScaleWidth - 10
sngHeight = Me.ScaleHeight - 10
Me.Line (sngTop, sngLeft)-(sngWidth, sngHeight), vbBlack, B
'See Line Method in the help files for more information.
End Sub