CSS often fields questions about troubleshooting Exchange 2007 Client Access Server (CAS) publishing rules using ISA Server 2006. The ForeFront TMG team blog has a great post: Troubleshooting OWA 2007 Publishing Rules on ISA Server 2006.
If you're just getting started with publishing Exchange 2007 using ISA Server 2006, here's one of our favorite docs, courtesy the ForeFront TMG team: Publishing Exchange Server 2007 with ISA Server 2006.
ISA Server 2006 SP1 includes support for SAN certificates, and some new features that make it a must-have upgrade. If you haven't upgraded to SP1 yet, you can find out more about these new features in this blog post by the ForeFront TMG team: ISA Server 2006 Service Pack 1 Features.