One popular application of VPNs (Virtual Private Networking) is to allow staff working from home, client sites, or other remote locations to connect in to the office network over the Internet using an encrypted tunnel. PPTP (Point-to-Point Tunneling Protocol) is Microsoft's protocol for this purpose, and Poptop implements it under Linux. Installing Poptop makes your Linux box appear to the outside world just like a Microsoft ISA Server, and because PPTP is, of course, natively supported under Windows, this is currently by far the most effective way of providing VPN access to remote Windows users.
The talk will consist of a brief introduction to Poptop, a walk-through of a Poptop installation and live demo, followed (hopefully!) by a discussion of the issues raised by Poptop, and VPNs more generally.
There's no second talk that I know of, but one of the usual suspects may volunteer one before Saturday, perhaps.