I'm working on a project to replace my organisation's aging Slackware gateway/router/firewall machine in our colo rack. Previously we used rc.firewall but we are now looking for something more modern and easily configurable. The requirements are:

• Act as a gateway router & firewall
• Port forwarding to a Terminal Server in the colo
• IP/traffic accounting, preferably accessible via SNMP (already using cacti for other servers)
• Possibility of acting as a PPTP server & routing these connections
• Is not an out-of-the-box Cisco product (don't have the finances or support to maintain it)

I'd prefer to use Ubuntu or some other Debian-based distro but something that integrates everything we're looking for is certainly an option if it offers all the desired features and is easy to configure.

Is there a simple set of packages that will provide me with the Firewall & Accounting features, or am I best served with a custom-built distro / other solution?