Get screen position of caret in an external application

Hi,

I'm trying to get the screen position of an external application that I have no control over (ie: Notepad). I then want to show a form at this position. I have code that is working, partially. The method get's called on every keystroke in the window (using an IME/TSF to capture these strokes). The form shows and moves to the to the right (the Left property changes) as I type, the problem is the window is no where near the caret. Here's the code I have:

        // Win32 Calls
        [StructLayout(LayoutKind.Sequential)]
        public struct RECT {
            public uint Left;
            public uint Top;
            public uint Right;
            public uint Bottom;
        };
        [StructLayout(LayoutKind.Sequential)]
        public struct GUITHREADINFO {
            public uint cbSize;
            public uint flags;
            public IntPtr hwndActive;
            public IntPtr hwndFocus;
            public IntPtr hwndCapture;
            public IntPtr hwndMenuOwner;
            public IntPtr hwndMoveSize;
            public IntPtr hwndCaret;
            public RECT rcCaret;
        };
        [DllImport("user32.dll", EntryPoint = "GetGUIThreadInfo")]
        public static extern bool GetGUIThreadInfo(uint tId, out GUITHREADINFO threadInfo);
       
        // Get the caret position
       public static RECT GetCaretPosition() {
            GUITHREADINFO gInfo = new GUITHREADINFO();
            gInfo.cbSize = (uint)Marshal.SizeOf(gInfo);
            GetGUIThreadInfo(0, out gInfo);
            return gInfo.rcCaret;
        }

As I said, setting the Form.Left and Form.Top properties to the gInfo.rcCaret.Left/Top properties causes the form to show far away from the actual caret position on screen. The Left property of the form does update as I type, however.

Any thoughts as to how I can get this to work?