SBS 2003 Problem with clien computers accessing the internet

I have a SBS 2003 server setup with dual network cards. I have done the wizard and connected the server to the intenet. The problem is the client pc’s cannot acces the internet. The server has full access, if you ping from a client it resolves the ip address of google, but gets no reply. so im sure its not a dns problem. ANy ides on resolving this?