private bool closeProc(string ProcName)
{
 bool result = false;
 System.Collections.ArrayList procList = new System.Collections.ArrayList();
 string tempName = "";

 foreach (System.Diagnostics.Process thisProc in System.Diagnostics.Process.GetProcesses())
 {
  tempName = thisProc.ProcessName;
  procList.Add(tempName);
  if (tempName == ProcName)
  {
   if (!thisProc.CloseMainWindow())
　　　　　　　　thisProc.Kill(); //当发送关闭窗口命令无效时强行结束进程     
    result = true;
  }
  }
  return result;
}

[DllImport("user32.dll", CharSet=CharSet.Auto)]  
public static extern int SendMessage(int hWnd, int msg, int wParam, int lparam);

 //SendMessage(hwnd1,WM_CLOSE,0,0); 
 //hwnd1是你用findwindow函数返回的句柄值
 //wm_close定义在winuser.h里面
 //0x0010是 WM_CLOSE的值
 SendMessage(hwnd1,0x0010,0,0);