Exchange 5 auto reply

How can I create an auto-reply message for acknowledging a received email? I’m running MS Exchange 5.0 with SP/2 on NT 4.0 SP/5. I do not want to use Outlook’s “Inbox Assistant” because there is no primary owner of the mailbox, and the client sidemust be powered on and working continuously. The reply message would is for a sales inquiry email that can be generated off of our Web site. Is there any way to do this from the server side? If not, are there any third party tools that incorporate this functionality? Thanks in advance!