//Check to see if this user exists
public bool UserExists(string username)
{
   DirectoryEntry de = GetDirectoryEntry();
   DirectorySearcher deSearch = new DirectorySearcher();

   deSearch.SearchRoot = de;
   deSearch.Filter = "(&(objectClass=user) (cn=" + username + "))";

   SearchResultCollection results = deSearch.FindAll();

   return results.Count > 0;
}

private String FindName(String userAccount)
{
   DirectoryEntry entry = GetDirectoryEntry();
   String account = userAccount.Replace(@"Domain\", "");

   try
   {
      DirectorySearcher search = new DirectorySearcher(entry);
      search.Filter = "(SAMAccountName=" + account + ")";
      search.PropertiesToLoad.Add("displayName");

      SearchResult result = search.FindOne();

      if (result != null)
      {
         return result.Properties["displayname"][0].ToString();
      }
      else
      {
         return "Unknown User";
      }
   }
   catch (Exception ex)
   {
      string debug = ex.Message;

      return "";
   }
}