get Mailbox usage using WMI without Admin rights

[garks]

I am using Exchange 2003(Exchange Hosting), C#.

I am trying to get Mailbox usage using WMI

But I follows the coding below, still cannot get the Mailbox usage.
Even though, I predefined the username and password.
Often gets "Access denied" while running the code.
I have tried to add the user to the \root\Microsoft ExchangeV2, and the
delegate control, but still cannot.
Is there anything I missing to add?
Or other methods that can access the mailbox usage?
Thanks in advanced

System.Manageme nt.ConnectionOp tions objconn = new
System.Manageme nt.ConnectionOp tions();
objconn.Imperso nation =
System.Manageme nt.Impersonatio nLevel.Imperson ate;
objconn.EnableP rivileges = true;
string cServername = "servername ";
System.Manageme nt.ManagementSc ope exmangescope = new
System.Manageme nt.ManagementSc ope(@"\\" + cServername + @"\root
\MicrosoftExcha ngeV2",objconn) ;
System.Manageme nt.ObjectQuery objquery = new
System.Manageme nt.ObjectQuery( "SELECT * FROM Exchange_Mailbo x");
System.Manageme nt.ManagementOb jectSearcher objsearch = new
System.Manageme nt.ManagementOb jectSearcher(ex mangescope,objq uery);
System.Manageme nt.ManagementOb jectCollection queryCollection 1 =
objsearch.Get() ;
string strDisplay;
foreach( System.Manageme nt.ManagementOb ject instmailbox in
queryCollection 1 )
{
strDisplay = instmailbox["MailboxDisplay Name"].ToString() + " " +
instmailbox["size"].ToString();
System.Console. WriteLine(strDi splay);
}