When you ping the
www.yahoo.com URL do you see it resolve to an IP address?
If it does not resolve to an IP address then there is a problem with your DNS settings. Please make sure that your adapters are marked correctly in WinGate and that there is a binding policy in the WinGate DNS service to bind to the internal adapter.
If the URL resolves to an IP address but you can't reach it then there is a problem connecting to/through WinGate. Are you able to ping the WinGate server. Are you able to ping the router through the server (WinGate's default gateway)?
Please make sure that the WinGate server's internal adapter does not have a default gateway listed, and unless you're running Active Directory the DNS server should also be left blank.
Let us know how you get on,