Clients cant connect to the internet

I have a small domain with small business server 2003. On the server I can connect to the internet, but on the client computers I cant connect to the internet. There are two networkcards on the server, and the clients use the internal card as a defult gateway. When I do tracert from the client I see that the client dont get routed to the other networkcard on the server... How can I fix this ? Can I set a route on the server that will fix this ?