Ok, well just guessing from the information in the orginal post, I would say that ISA is going to be used as the network gateway. I am no expert at ISA server, but I have set it up on a number of Small Business servers.

The configuration should be set up so that all users have to go out via the ISA server. Meaning that they shouldnt have direct access to the ASDSL router, or any hardware firewall/gateway.

Typically this is done via two NIC's in the ISA server, one for intranet, one for internet usage. All workstation get pointed to the ISA server for external access. The second NIC is configured as the local gateway. All incomming traffic (VPN) gets passed thru the ASDSL router, thru any hardware firewall, and authorized via the ISA VPN client. In most cases, ISA server acts like a hardware firewall, via the second NIC. There really isnt any reason to use both the router VPN and the ISA VPN.

Of course if you have youre gateway attached directly to the same switch as your LAN, then users can easily bypass all the ISA settings and security.

ISA server isnt junk, and lots of companies use it. It wasnt "hacked together".