The following code snippet (posted in the Windows Forms FAQ forums) shows how you can prevent a user from moving a form at run time:

protected override void WndProc( ref Message m ) 
{ 
  const int WM_NCLBUTTONDOWN = 161; 
  const int WM_SYSCOMMAND = 274; 
  const int HTCAPTION = 2; 
  const int SC_MOVE = 61456; 

  if ( (m.Msg == WM_SYSCOMMAND) && (m.WParam.ToInt32() == SC_MOVE) ) 
    return; 
  if ( (m.Msg == WM_NCLBUTTONDOWN) && (m.WParam.ToInt32() == HTCAPTION) ) 
    return; 

  base.WndProc( ref m ); 
}  

Contributed from George Shepherd's Windows Forms FAQ