http://www.cnblogs.com/wintalen/archive/2011/01/04/1925274.html
string htmInfo = "readme.htm";
System.Diagnostics.Process.Start("iexplore.exe", Application.StartupPath + @"\HTML\" + htmInfo);
//如果是调用系统默认打开方式,则下面的方式就可以了
//System.Diagnostics.Process.Start(Application.StartupPath + @"\HTML\" + htmInfo);