this is how i accomplished this, check to see if it works for you:

VB Code:
  1. Declare Function ShowWindow Lib "user32" (ByVal hWnd As Int32, ByVal nCmdShow As Int32) As Int32
  2.  
  3.         Dim proc() As Process
  4.         proc = Process.GetProcessesByName(Application.ProductName)
  5.         If proc.Length > 1 Then
  6.  
  7.             If proc(1).Id = Process.GetCurrentProcess.Id Then
  8.                 ShowWindow(proc(0).MainWindowHandle.ToInt32, 9)
  9.                 Microsoft.VisualBasic.AppActivate(proc(0).Id)
  10.  
  11.             Else
  12.                 ShowWindow(proc(1).MainWindowHandle.ToInt32, 9)
  13.                 Microsoft.VisualBasic.AppActivate(proc(1).Id)
  14.             End If
  15.             Exit Sub
  16.         End If