This should do it:

    ...
    using System.Runtime.InteropServices;
    using System.Diagnostics;

    ...

public class foo()
{
    ...

    [DllImport ("user32")]
    internal static extern int GetWindowText (int hWnd, String text, int nMaxCount);

    [DllImport ("user32.dll")]
    public static extern int GetWindowTextLength (int hWnd);

    [DllImport ("user32.dll")]
    public static extern int FindWindow (String text, String class_name);

    [DllImport ("user32.dll")]
    public static extern int FindWindowEx (int parent, int start, String class_name);

    [DllImport ("user32.dll")]
    public static extern int GetWindow (int parent, uint cmd);

    public List<int> FindTitlelessWindows()
    {
        List<int> titleless = new List<int> ();

        Process [] procs = Process.GetProcesses ();
        IntPtr hWnd;

        foreach (Process proc in procs)
        {
            hWnd = proc.MainWindowHandle;
            if (hWnd != IntPtr.Zero)
            {
                TraverseHierarchy (hWnd.ToInt32 (), 0, titleless);

            }
        }

        foreach (int i in titleless)
        {
            System.Console.WriteLine (i);
        }

        return titleless;
    }

    public void TraverseHierarchy (int parent, int child, List<int> titleless)
    {
        String text = "";
        GetWindowText (parent, text, GetWindowTextLength (parent));
        if (String.IsNullOrEmpty (text))
        {
            titleless.Add (parent);
        }

        TraverseChildern (parent, titleless);
        TraversePeers (parent, child, titleless);

    }

    public void TraverseChildern(int handle, List<int> titleless)
    {
        // First traverse child windows
        const uint GW_CHILD = 0x05;
        int child = GetWindow (handle, GW_CHILD);
        if (0 != child)
        {
            TraverseHierarchy (child, 0, titleless);

        }
    }

    public void TraversePeers(int parent, int start, List<int> titleless)
    {
        // Next traverse peers
        int peer = FindWindowEx(parent, start, "");
        if (0 != peer)
        {
            TraverseHierarchy (parent, peer, titleless);
        }

    }
}

Take a look at the EnumChildWindows function.

I think that if you pass in the pointer of the main window (i.e. desktop) to this function, you will be able to get a list of all windows and their child windows.

In combination with FindWindow it should be possible to get the handle to the window you want once you locate an expected child control.

Something like this should work, not tested

[DllImport("user32", CharSet = CharSet.Auto, SetLastError = true)]
internal static extern int GetWindowText(IntPtr hWnd, [Out, MarshalAs(UnmanagedType.LPTStr)] StringBuilder lpString, int nMaxCount);

[DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]
public static extern int GetWindowTextLength(IntPtr hWnd); 

....
Process[] procs = Process.GetProcesses();
IntPtr hWnd;
foreach(Process proc in procs)
{
    hWnd = proc.MainWindowHandle;
    if (hWnd != IntPtr.Zero)
    {
        int length = GetWindowTextLength(hWnd);
        StringBuilder sb = new StringBuilder(length + 1);
        GetWindowText(hWnd, sb, length);
        if (String.IsNullOrEmpty(sb.ToString())
        {
            // we have a window with no title!
        }
    }
}

http://msdn.microsoft.com/en-us/library/ms633558(VS.85).aspx

WindowFromPoint returns a handle, or null if no window is underneath your cursor. Could this be used, or are you trying to automate the process?

Here you can find a library to deal with windows API stuff in managed code.
Download the dll and reference it in your project and from there on it s very easy to get any information on any window you want;

 void ForAllSystemWindows()
        {
            foreach (SystemWindow window in SystemWindow.AllToplevelWindows)
            {
                if (window.Title == string.Empty)
                {
                    //Found window without title

                    //Get window handle
                    IntPtr windowhandle  = window.HWnd;

                    //Do other stuff ..
                }
            }
        }