|You could create a VPN connection to a computer connected to the internet via dialup, but the resultant speed will be the same as if you dialed directly into the PC as I described above.|
When talking about networks and bandwidth, your bandwidth is always controlled by the slowed component. Which is to say, you will always connect at the speed of the slowest connection.
So, in the case of VPN'ing in to a computer that's connected to the internet via dialup, your limited to their connection rate. Which would be the exact same as if you dialed into them directly.