public class MyPictureBoxWheel : PictureBox
{
    public event MouseEventHandler MouseWheel;
    protected override void OnMouseWheel(MouseEventArgs e)
    {
        base.OnMouseWheel(e);
        if (MouseWheel != null) MouseWheel(this, e);
    }
}

------解决方案--------------------
http://download.csdn.net/source/2701596
应该对你有帮助

------解决方案--------------------
C# code

//鼠标滚轮事件
        void pictureBox1_MouseWheel(object sender, System.Windows.Forms.MouseEventArgs e)
        {
             Size t = pictureBox1.Size;
             if (e.Delta == -120)
             {
                 pictureBox1.Size = new Size(t.Width - 120, t.Height - 120);                   
             }
             else if (e.Delta == 120)
             {                    
                 pictureBox1.Size = new Size(t.Width + 120, t.Height + 120);
             }
        }