<Grid Name="gd">
  <Button Width=90 Height=30 Name="btn">button</Button>
</Grid>

public SystemMap()
{
   InitializeComponent();
   btn.MouseLeftButtonDown += btn_MouseLeftButtonDown;
   btn.MouseMove += btn_MouseMove;
   btn.MouseLeftButtonUp += btn_MouseLeftButtonUp;
}

Point pos = new Point();
void btn_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
  Button tmp = (Button)sender;
  pos = e.GetPosition(null);
  tmp.CaptureMouse();
  tmp.Cursor = Cursors.Hand;
}

void btn_MouseMove(object sender, MouseEventArgs e)
{
   if (e.LeftButton==MouseButtonState.Pressed)
   {
      Button tmp = (Button)sender;
      double dx = e.GetPosition(null).X - pos.X + tmp.Margin.Left;
      double dy = e.GetPosition(null).Y - pos.Y + tmp.Margin.Top;
      tmp.Margin = new Thickness(dx, dy, 0, 0);
      pos = e.GetPosition(null);
   }
}

void btn_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
     Button tmp = (Button)sender;
     tmp.ReleaseMouseCapture();
}