Place the following code in the paint event of the form. Ensure that you have a form-wide Graphics object declared, named grph. This is not the most efficient way of doing this, but it gets you started.

VB Code:
  1. grph = Me.CreateGraphics
  2.         grph.Clear(Me.BackColor)
  3.  
  4.         Dim pn As New Pen(Color.Black)
  5.  
  6.         grph.DrawLine(pn, 0, 0, Me.ClientSize.Width, Me.ClientSize.Height)
  7.         grph.DrawLine(pn, 0, Me.ClientSize.Height, Me.ClientSize.Width, 0)
  8.  
  9.         grph.Dispose()