WebProNews

public static string GetSubDomain(Uri url)
{
if (url.HostNameType == UriHostNameType.Dns)
{
string host = url.Host;
if (host.Split('.').Length > 2)
{
int index = host.IndexOf(".");
return host.Substring(0, (index - 1));
}
}

return null;
}

Handy dandy.  Thanks.