For the below script to work, you need the AcctCrt COM components to be installed. You can download this component form the Microsoft site.

strDomainNT4 = "TOOLS4EVER"
strUsername = "avdvorst"
strEx55Server = "EXCHANGE"
strMailboxPath = "DN of your recipient container"
strSite = "Name of site"
strOrg = "Name of organization"

Set objAcctMgmt = CreateObject("MSExchange.AcctMgmt")
'prepare Exchange security descriptor (needs WinNT binding so make sure the user account has been replicated among all DCs
RetVal = objAcctMgmt.GetSidFromName(strDomainNT4, strUsername, arrSID)
RetVal = objAcctMgmt.GenerateSecDescriptor(strDomainNT4, strUsername, arrSD)

'connect to the container where you want the mailbox created
Set objMBContainer = GetObject("LDAP://" & strEx55Server & "/" & strMailBoxPath)
'create the actual mailbox object
Set objMB = objMBContainer.Create("OrganizationalPerson", "cn=" & strUser)
'set the mailbox object properties
objMB.Put "Assoc-NT-Account", (arrSID)
objMB.Put "NT-Security-Descriptor", (arrSD)
objMB.Put "uid", strUsername
objMB.Put "mailNickname", strUsername
objMB.Put "MDB-Use-Defaults", True
objMB.Put "MAPI-Recipient", True
strMDB = "cn=Microsoft Private MDB,cn=" & strEx55Server & _
",cn=Servers,cn=Configuration,ou=" & strSite & ",o=" & strOrg
objMB.Put "Home-MDB", strMDB
strMTA = "cn=Microsoft MTA,cn=" &
strEx55Server & _
",cn=Servers,cn=Configuration,ou=" & strSite & ",o=" & strOrg
objMB.Put "Home-MTA", strMTA
objMB.SetInfo