Hi, Maybe it is too obviously, but I still post this.
Basic: Address 0.0.0.0 is the address the DHCP-client have before it contact the DHCP-server for an IP-lease, and it broadcast an IP-request to ANY DHCP-server, the first who answers with an IP-address the client ussually takes.
So what I'm thinking, is that your client doesn't get an IP-address, and why not? are you sure you have free IP at your DHCP server? But OK, since this happened when you installed ISA Client Firewall, it should have something to do with that, have you checked the bindings on your NIC? what happends if you set a static IP on the client, can you still not ping your gate way etc?
One more question, is your DHCP server on the same network segment as the client? or is the DHCP server on the other side of the ISA server (if you know what I mean?) /John