Exchange Monitoring tool

Does anyone know where I could find a Free, or trial/share-ware Exchange monitoring tool that will allow me to identify the orgin and destination of attachments? We already have Netshield, which will identify and quarantine all kinds of attachments.

I am just interested in finding out who was responsible for sending what attachment to what recepient across our network, or from the outside inif possible, but internally is more important.

Runnning Exchange 5.5/NT server 4.0, Service PAck 6a.

Thanks.

Paul M. Chavez