Using PostMessage/SendMessage to send keys to c# IE WebBrowser

[DllImport("user32.dll")]
    [return: MarshalAs(UnmanagedType.Bool)]
    static extern bool PostMessage(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll")]
    static extern int SendMessage(IntPtr hWnd, uint msg, IntPtr wParam, IntPtr lParam);

    const uint WM_KEYDOWN = 0x0100;
    const uint WM_KEYUP = 0x0101;
    const uint WM_CHAR = 0x0102;
    const int VK_TAB = 0x09;
    const int VK_ENTER = 0x0D;
    const int VK_UP = 0x26;
    const int VK_DOWN = 0x28;
    const int VK_RIGHT = 0x27;

    //According to SPY++ in IE

    //ENTER key is
    // P KEYDOWN
    // P CHAR
    // S CHAR
    // P KEY_UP

    //TAB key is
    // P KEYDOWN
    // P KEYUP

    //DOWN, UP, RIGHT, LEFT is
    // P KEYDOWN
    // S KEYDOWN
    // P KEYUP

    //Letters is
    // P KEYDOWN
    // S KEYDOWN
    // P CHAR
    // S CHAR
    // P KEYUP

    private void SendEnter()
    {
        PostMessage(this.Handle, WM_KEYDOWN, (IntPtr)VK_ENTER, IntPtr.Zero);
        PostMessage(this.Handle, WM_CHAR, (IntPtr)VK_ENTER, IntPtr.Zero);
        SendMessage(this.Handle, WM_CHAR, (IntPtr)VK_ENTER, IntPtr.Zero);
        PostMessage(this.Handle, WM_KEYUP, (IntPtr)VK_ENTER, IntPtr.Zero);
    }

    private void SendTab()
    {
        PostMessage(this.Handle, WM_KEYDOWN, (IntPtr)VK_TAB, IntPtr.Zero);
        PostMessage(this.Handle, WM_KEYUP, (IntPtr)VK_TAB, IntPtr.Zero);
    }

    private void SendArrowKey(int key)
    {
        PostMessage(this.Handle, WM_KEYDOWN, (IntPtr)key, IntPtr.Zero);
        SendMessage(this.Handle, WM_KEYDOWN, (IntPtr)key, IntPtr.Zero);
        PostMessage(this.Handle, WM_KEYUP, (IntPtr)key, IntPtr.Zero);
    }

    private void SendChar(int key)
    {
        //Keydown wParam values are 0x020 less than WM_CHAR wParam
        PostMessage(this.Handle, WM_KEYDOWN, (IntPtr)(key - 0x020), IntPtr.Zero);
        SendMessage(this.Handle, WM_KEYDOWN, (IntPtr)(key - 0x020), IntPtr.Zero);
        PostMessage(this.Handle, WM_CHAR, (IntPtr)key, IntPtr.Zero);
        SendMessage(this.Handle, WM_CHAR, (IntPtr)key, IntPtr.Zero);
        PostMessage(this.Handle, WM_KEYUP, (IntPtr)(key - 0x020), IntPtr.Zero);
    }