isa and client issue

i recently installed isa 2k6 on a win2k3 server, i have 3 nics installed in the box 1 DHCP server, another for internal and 1 more for external. i have my server handing out ips to clients, and i can access the internet from the server but i cant access it from my clients,i cant even ping the dhcp server or the internal netowrk nic? any ideas? i also have a d-link router giving an ip to the external card.. i tried every ip for dns the d-link router’s, the internal nic, and also the isp’s dns servers and i get nothing when i configure those address for my clients DNS server.