So far, there have been several good suggestions.You will definitely want to put in a Default Route Statement as mentioned before.Also, if you have access to the Router on the Outside of the PIX, you will want to clear it's ARP Table. If you are not...

By default the PIX will permit all outbound traffic through. It will also permit all reply traffic to the outbound traffic through.The PIX will however block all incoming traffic unless you create an Access List to permit certain traffic through.Onc...