how to extract html in asp.net

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ASP.NET

hi ,
i want to extract all the categories and sub categories from this link. anyone please tell me how i can do so , please give me hint
http://www.codeproject.com/script/Content/SiteMap.aspx[^]

im practising webclient , PLEASE ONLY GIVE ME REGEX FOR IT. all categories and subcategories should be gathered


following is the code i have wrote so far :i want on ly regex to pass on it to gather all data

public ExtractHtml(String url)
        {
            client = new WebClient();
            strm = client.OpenRead(url);
            StreamReader strrdr = new StreamReader(strm,Encoding.ASCII);
            code = strrdr.ReadToEnd();

        }
        public List<string> Extract(String regex)
        {
            lines = new List<string>();
            Regex rgx = new Regex(regex, RegexOptions.IgnoreCase);
            MatchCollection cl =  rgx.Matches(code);
            foreach (Match item in cl)
            {
                lines.Add(item.Value);
            }
            return lines;
        }

i want to extract text from this

<a id="ctl00_MC_TCRp_ctl00_TCNL" href="/Chapters/1/Desktop-Development.aspx">Desktop Development</a>

<li>
<a id="ctl00_MC_TCRp_ctl00_TSRp_ctl01_TSNL" href="/KB/buttons/">Button Controls</a>

</li>

<li>
<a id="ctl00_MC_TCRp_ctl00_TSRp_ctl02_TSNL" href="/KB/clipboard/">Clipboard</a>

</li>

<li>
<a id="ctl00_MC_TCRp_ctl00_TSRp_ctl03_TSNL" href="/KB/combobox/">Combo & List Boxes</a>

</li>

<li>
<a id="ctl00_MC_TCRp_ctl00_TSRp_ctl04_TSNL" href="/KB/dialog/">Dialogs and Windows</a>

</li>

<li>
<a id="ctl00_MC_TCRp_ctl00_TSRp_ctl05_TSNL" href="/KB/gadgets/">Desktop Gadgets</a>

</li>