Exchange Server client through ISA

Recently we have moved to ISA Server from Proxy Server 2.0. Everything appears to be running great except for one thing, our connection between Outlook and Exchange Server. All our workstations connect to Exchange Server 5.5 located at our ISP. We use the lmhosts file to configure the Exchange client so Outlook can connect. I have configured the packet filter for port 135, 1225 and 1226. I searched TechNet and only found one article, “XADM: Setting TCP/IP ports for Exchange and Outlook Client Connections Through a Firewall”. The article has you making registry changes on the client and opening the above ports. However, our workstations do not have the registry key that the article talks about. HELP I NEED MY EMAIL!