Authentification Help

I have created a script that authenticates to an Active Directory server. This script works when I try to login, but the problem is that I have to bind to be able to get "my" dn to be able to authenticate, but I need authenticate first to be able to get "my" dn. Chicken before the egg problem. In the ldap_bind(), I have entered "my" dn to be able to authenticate for now, but with this I am the only person that would be able to login. I could bind to the server twice, once to get an individuals "dn" , set the variable, and then once I have the "user's" dn I could bind again as that user, but this seems like it would cause a lot of overhead. Does anyone have a better way to do this than bind twice? $dn = "OU=Anoka-Hennepin,DC=ah,DC=isd11";

    $filter = "(samaccountname=" . $username . "*)";

    $ad = ldap_connect("ldap://172.22.1.20")
          or die("Couldn't connect to AD!");

    $bd = ldap_bind($ad, "CN=Tuller\, Mike,OU=Staff,OU=LCDC,OU=Anoka-Hennepin,DC=ah,DC=isd11",$password)
          or die("Couldn't bind to AD!");

    $result = ldap_search($ad, $dn, $filter);

    $entries = ldap_get_entries($ad, $result);

    for ($i=0; $i<$entries["count"]; $i++)
    {
        echo $entries[$i]["dn"];
    }