using System; 
using System.IO; 
using System.Collections.Generic; 
using System.Windows.Forms; 
using System.Diagnostics; 
 
namespace WindowsApplication2MMS 
{ 
    static class Program 
    { 
        private static bool IsExistProcess() 
        { 
            bool result = false; 
            Process[] p = Process.GetProcessesByName(Path.GetFileNameWithoutExtension
(Application.ExecutablePath)); 
            if (p != null && p.Length > 1) 
            { 
                result = true; 
            } 
            return result; 
        }                     
 
   //    public Form1 mainform = null; 
   //    public static SplashScreen loadfrom = new SplashScreen(); 
        /// <summary> 
        /// 应用程序的主入口点。 
        /// </summary> 
        [STAThread] 
        static void Main() 
        { 
            Application.EnableVisualStyles(); 
            Application.SetCompatibleTextRenderingDefault(false); 
 
            if (!IsExistProcess()) 
                Application.Run(new Form1()); 
            else 
                Application.Exit(); 
        //  Application.Run(new check()); 
        //  Application.Run(new imageshow()); 
        } 
    } 
} 

可参考http://www.cnblogs.com/Fooo/archive/2008/09/25/1298455.html