davidp, I am pretty familiar with Pinnacle Studio.
Whoever told you that you cannot add multiple projects to a single disc was right, in respect to that software.
But where there is will, there is a way so here's my answer to this:
author your projects with Pinnacle Studio, as you usually do, but instead of using the built-it disc authoring tool, produce the project as an image onto the hard drive (in the Advanced options dialog select Create disc content but don't burn). After it's done, burn it to a DVD and leave it open-session. Next time your produce something, follow the same procedure... and so on, until the disc is full. Then, and only then, should you buy another blank DVD . Cheap isn't it?