few things are needed for your to access Internet:
route, in your case, if you enabled Add Default Route, in PPTP client, this shoudl be added for you.
NAT: or masquerade, this trancelate your LAN address to your WAN IP address, in your case it is whatever IP address you get from you VPN connection.
3, DNS: this can be either your ISP’s DNS, or just Google.
these 3 things are needed for your router to access the Internet, can you ping 8.8.8.8 from the router? can you ping Google.com from the router?