Use REPORTS onPage funct
I needed something simillar, so I experimented with the lines from VB and those can be very handy:
I needed a line that goes accross an entire report so I set the reports OnPage function and put in:
Private Sub Report_Page()
DrawWidth = 15 '' I needed a thick line so I set it to 15
y1 = TotGrp * 330 '' for every row of report height in pixels, you can set whatever you like
Me.Line (5092, 3580 + y1)-(11110, 3580 + y1), 0
DrawWidth = 15
Me.Line (5092, 3580 + y1)-(60, 11500), 0
End Sub