Build an enterprise application for a customer with aprox. 100 Clients ???

Question

HI!!! If you would happen to get the chance to build an enterprise application for a customer with aprox. 100 Clients (…and increasing) which technology and architecture would you choose. The security policy is pretty strong so we would have actually only port 80 available. Besides that no deployment effort on client side is desirable. There is a 100Mbit LAN and this new application would be deployed on the intranet (internal network). The GUI of this application should be very rich and fast like win32 applications. What would you propose in order to fulfil those requirements. Any hints, links and ideas will be highly appreciated Regards, gicio