Changing AD Properties with Powershell

Hi all,
 
Not much activity here?
 
I am trying to a powershell script which users a CSV file which contains the users SamaccountName, Department and Title.  At the moment I have the below which works if I use the CN to find them but this isnt a unquie identifer so I need to use the samaccountname, any ideas on how this can be done?  I think I aslo need it to connect to the default ad route rather than taking the path from a CSV file.
 
$users = import-csv users.csv
foreach($row in $users)
{
$dn = $row.dn
$user=[ADSI]LDAP://$dn
 
$title = $row.title
$department = $row.department
 
$user.put("title", $title)
$user.put("department", $department)


$user.SetInfo()
}
 
 
Typed this up pretty quick so sorry if it doesnt make much sense.

I'm confused. It looks (from the naming used) that you are using the DN to get the account. Is that not sufficient?