Same as all scripts working with Exchange 5.5, download and install the AcctCrt COM components from Microsoft. Only issue with this script is that it's not easy to reverse the operation. Once the mailbox is hidden, it is also hidden from LDAP queries. The only way to get it back is to do a special LDAP login (using clear-text password, so you really don't want to do that).

strExchangeServer = wscript.arguments(0)
strMailboxLDAP = wscript.arguments(1)
strMailboxLDAP = "LDAP://" & strExchangeServer & "/" & strMailboxLDAP

Set objAcctMgmt = CreateObject("MSExchange.AcctMgmt")
Set objMailbox = GetObject(strMailboxLDAP)

objMailbox.Put "Hide-From-Address-Book",True