From: Aliso Viejo, Ca, USA
i have this same problem...i followed the directions from tom's notes on allowing ping requests and still i'm unable to ping external addresses from any client and the isa server itself. i enabled ip filtering and ip routing and i even setup the filtering to allow all icmp traffic and still i'm unable to ping external internet addresses.
See if this helps - another tip, as a test turn on "Log packets from allow filters". This will record your newly created allow filter rules working (or not).
In the meantime, I've solved the problem. At least for the configuration that I have. I have a DHCP server and there, in the Scope options I've changed the Default Gateway's adress, from the real one (the router that connects to the T1 line) to the Internal Network Card on my ISA server. Now all the DHCP clients get this configuration along with their lease address, and I CAN PING outside the firewall.