using System.DirectoryServices;  //add to references

public static List<string> GetComputers()
{
    List<string> ComputerNames = new List<string>();

    DirectoryEntry entry = new DirectoryEntry("LDAP://YourActiveDirectoryDomain.no");
    DirectorySearcher mySearcher = new DirectorySearcher(entry);
    mySearcher.Filter = ("(objectClass=computer)");
    mySearcher.SizeLimit = int.MaxValue;
    mySearcher.PageSize = int.MaxValue;

    foreach(SearchResult resEnt in mySearcher.FindAll())
    {
        //"CN=SGSVG007DC"
        string ComputerName = resEnt.GetDirectoryEntry().Name;
        if (ComputerName.StartsWith("CN="))
            ComputerName = ComputerName.Remove(0,"CN=".Length);
        ComputerNames.Add(ComputerName);
    }

    mySearcher.Dispose();
    entry.Dispose();

    return ComputerNames;
}