This project requires the complete integration of multiple Open Source tools and applications to create a "Virtual Router" configuration or System Image (ISO) that will contain the following capabilities:
Routing, NAT, Firewall, IPSec VPN Tunnel (Vyatta Router)
SSL, PPTP onDemand VPN with Radius Support (OpenVPN or other)
Antivirus scanning and removal (ClamAV)
Spam scanning and removal (SpamAssassin)
Intrusion Detection (Snort or other)
The final product will require a web front end that allows configuration of all these tools from a single interface as well as ongoing monitoring and alerting setup.
Several of these tools use similar underlying components so you will need to be experienced with Linux and routing to ensure one component does not disable the other.
See attached doc for an outline of the setup.