PPTP VPN Testing

I am trying to comnnect an XP-prof-SP2 Box from laptop. the Xp-prof box is behind a Linksys WRV54G VPN Router.

Every Time I forward 1723/47 port to the box IP the Router Crashes.

Also If I connect straight, How Do I browse network and website. I need a comprehensive idea of testing even the simplest pptp VPN.