Firstly let me start by describing what I have:
I am running a Windows Server 2003 machine as a VPN server using RRAS (no special encryption, just a standard PPTP connection) between this and the internet I have a Cisco 2600 series router which routes all non-local packets to my Cisco PIX 515 firewall. The firewall has the necessary configuration to permit the VPN and the router is configured to bounce packets properly - this is evident because internal clients can browse the web and do other stuff on-line. I am also running a windows 2000 server that is part of the same domain with ISA 2000 server running as a proxy to facilitate authenticated access to the internet for my internal clients.
I have a Windows XP SP2 machine at home which has a VPN client installed on it. When I fire up the VPN it connects perfectly and I can ping/browse the servers on the remote location without any problems. the RRAS server allocates the Windows XP VPN client an IP address which seems to work fine until the point where I try to get out onto the internet through the VPN connection. Regardless of whether I try to use the proxy server address to get out or just leave it blank I just get no kind of internet access at all. Does anyone have any experience of this or have any suggestions?.