Debian with PPTP Server

Dear All

My scenario is

Debian with PPTP Server in which I am able to connect to through other machines. Ive enable echo 1 > /proc/sys/net/ipv4/ip_forward and through client machine i can browse internet as well

I created another pptp client in debian server which connects to another service provider. Now I want my users which are connecting to this debian pptp server to use internet which I m getting on this server from another ISP (through a pptp client)
I already tried All Traffic Through Tunnel script but it didnt helped me out.

Please help

Thanks