Something

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Threading;
namespace InGameOverlay
{
    public partial class Form1 : Form
    {

        IntPtr Game;
        Graphics GameOverlay;
        Thread GameOverLayThread;

        [DllImport( "user32.dll" )]
        public static extern IntPtr FindWindow(
            string lpClassName,	 // pouinter to class name
            string lpWindowName // pouinter to window name
        );

        public Form1() {
            InitializeComponent();
            Game = FindWindow( null, "Counter-Strike" );
            GameOverlay = Graphics.FromHwnd( Game );
            
        }

        public void DrawTime() {
            String Text = "00:12:32 PM";
            Font Verdana = new Font( "Verdana", 7, FontStyle.Bold );
            SolidBrush BrushGold = new SolidBrush( Color.Gold );
            SolidBrush BrushBlack = new SolidBrush( Color.Black );
            PointF FrontPoint = new PointF( 29.0F, 120.0F );
            PointF BehindPoint = new PointF( 30.0F, 121.0F );
            GameOverlay.DrawString( Text, Verdana, BrushBlack, BehindPoint );
            GameOverlay.DrawString( Text, Verdana, BrushGold, FrontPoint );
            GameOverlay.Dispose();
        }

        private void button1_Click( object sender, EventArgs e ) {
            GameOverLayThread = new Thread( DrawTime );
            GameOverLayThread.Start();
        }
    }
}