// Declare new DirectoryEntry and DirectorySearcher
DirectoryEntry domainRoot = new DirectoryEntry("LDAP://rootDSE");
string rootOfDomain = domainRoot.Properties["rootDomainNamingContext"].Value.ToString();
DirectorySearcher dsSearch = new DirectorySearcher(rootOfDomain);

// Set the properties of the DirectorySearcher
dsSearch.Filter = "(objectClass=Computer)";
dsSearch.PropertiesToLoad.Add("whenCreated");
dsSearch.PropertiesToLoad.Add("description");
dsSearch.PropertiesToLoad.Add("operatingSystem");
dsSearch.PropertiesToLoad.Add("name");

// Execute the search
SearchResultCollection computersFound = dsSearch.FindAll();

SortOption sortedResults = new SortOption("whenCreated", SortDirection.Descending);
dsSearch.Sort = sortedResults;

public class SearchResultComparer : Comparer<SearchResult>
{
    public override int Compare(SearchResult x, SearchResult y)
    {
        //Compare two SearchResult instances by their whenCreated property
    }
}

List<SearchResult> SearchResultList = new List<SearchResult>(computersFound);
SearchResultList.Sort(new SearchResultComparer());

new DirectorySearcher(entry)
      {
        Sort = new SortOption("cn", SortDirection.Ascending),
        PropertiesToLoad = {"cn"}
      };