I am implementing a network with an ASA 5520 and an ISA server. I would like to hear input from people who might have done this before as to what the best setup would be for this? Having two firewalls would enable a layer of protection behind the perimeter for internal network users. I am thinking of routing all traffic from a layer 3 switch to the ISA server and then to the ASA. I would run traffic through the ISA and NAT all of the traffic at the ASA, as well as terminate VPNs. Is there some kind of way to set up the ISA in some sort of transparent setup?

Please forgive me if this seems like a dumb question, I am a Cisco guy all the way.

Also, I know this isn't a microsoft forum but I know you can't go wrong with the net pros:) Thanks!