How to : Given HWND, discover if window is Modal or not

For any given window I handle, I need a way to find out whether or not the given window is Modal.

Far as I can tell, there are no methods that do exactly that, which is why I need some clever workaround to work this out!

Help is appreciated!

EDIT : Why is my GetWindow(,GW_OWNER) failing? :(

    [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
    internal static extern IntPtr FindWindow(string lpClassName, string lpWindowName);
    [DllImport("user32.dll", SetLastError = true)]
    internal static extern IntPtr GetWindow(IntPtr hWnd, GetWindow_Cmd uCmd);
    [DllImport("user32.dll", ExactSpelling = true)]
    internal static extern IntPtr GetAncestor(IntPtr hwnd, GetAncestor_Flags gaFlags);
    [DllImport("user32.dll", SetLastError = false)]
    internal static extern IntPtr GetDesktopWindow();
    [DllImport("user32.dll", SetLastError = true)]
    internal static extern int GetWindowLong(IntPtr hWnd, int nIndex);

    const UInt32 WS_DISABLED = 0x8000000;


    internal enum GetAncestor_Flags
    {
        GetParent = 1,
        GetRoot = 2,
        GetRootOwner = 3
    }

    internal enum GetWindow_Cmd : uint
    {
        GW_HWNDFIRST = 0,
        GW_HWNDLAST = 1,
        GW_HWNDNEXT = 2,
        GW_HWNDPREV = 3,
        GW_OWNER = 4,
        GW_CHILD = 5,
        GW_ENABLEDPOPUP = 6
    }



IntPtr _inspHwnd = FindWindow("rctrl_renwnd32", inspector.Caption); // searching for a window with this name
        if (_inspHwnd.ToInt32() != 0) // found window with this name
        {
            IntPtr _ownerHwnd = GetWindow(_inspHwnd, GetWindow_Cmd.GW_OWNER);
            if (_ownerHwnd.ToInt32() != 0)
            {
                IntPtr _ancestorHwnd = GetAncestor(_ownerHwnd, GetAncestor_Flags.GetParent);
                if (_ancestorHwnd == GetDesktopWindow())
                {
                    if (GetWindowLong(_ancestorHwnd, -16) == WS_DISABLED) 
                    { 
                        // i