<UrlRewrite>
    <Rule Look="word-([0-9]+).aspx" Send="default.aspx?classid=0&amp;id=$1" />
    <Rule Look="word-([0-9]+)-([0-9]+).aspx" Send="default.aspx?classid=0|$1&amp;id=$2" />
</UrlRewrite>

            string content = "default.aspx?classid=0&id=10";
            System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex(@"(?<=&id=)[\d]+");
            System.Text.RegularExpressions.Match m = reg.Match(content);
            MessageBox.Show("word-"+m.Value+".aspx");

------解决方案--------------------

把Look的([0-9]+)和Send的$对调，Send的&amp;改为&，再Replace