Oliver, you have to be more detailed and specific.
What are you trying to teach?
To what kind of audience?
Does the DVD have to be interactive or just a passive series of lectures by chapter?
Does the interactivity need to have features like quizzes?
Do you want the quizzes to direct viewers to more detailed learning based on their quiz answers?
List five things the audience should know or be able to do after watching this DVD.
Now you have just the minimal beginnings of a description of what you're trying to accomplish. There are several tools and techniques for doing this kind of work, not just authoring a DVD, but there's also what they call mutimedia authoring, which can get quite complex, taking a lot of expertise to build something in, say, Macromedia Director.
On the other, simplistic end of the scale, you can build powerpoint stacks with hyperlinks that can do everything an interactive DVD can do, and automatically convert into interactive web pages. How you approach it depends on many factors including budget and schedule and the ultimate results you're looking to achieve.
My first interactive DVD authoring experiece was rather demanding: Eight skits to set up situations, each then had a quiz with four possible answers. Wrong answers took you to an explanation of why that particular answer was wrong, then looped back to let you take the quiz again. If you answered every question right the first time, the links carried you thru each chapter in turn to a congratulations video. You only advanced to the next chapter by picking the right answer, or menuing-out to the main menu and picking another chapter.
Even though I pre-built a lot of the pieces in final cut, the "logic map" for the final project still looked like a bowl of noodles, and took days to build and test.
You can add sections of data files to an authored DVD, PDF files and slides that viewers with computers can access and print out for quizzes and certificates and such. People watching on a DVD player and TV can't access this content.
I don't know if buying a green screen is the first thing that comes to mind when developing an e-learning dvd. You need to decide what kind of DVD are you going to make. Is it for playback on any set top DVD player or only for playback on PCs? What about mac? Your decision would dictate the approach.
If you choose the set-top DVD route, then any advanced DVD author could help you out. It will likely require some advanced scripting knowledge.
On the other hand, for PC playback, a flash developer might be best. You may have one of them laying around.