Hi
The DVD generation part of videopad only writes the project to the disc in a single playable form. It will not add menus, play buttons etc. or add more than one project to the disc. Indeed, there have been a few posts saying that it doesn't complete the disc.
I would suggest the best way is to save your finished project/s to your PC as separate avis (or similar) and then use a third party dedicated DVD creator to produce your DVD. This way you can have previews, menus and choice buttons.
If you have Windows movie maker then you will probably also have Windows DVD maker which will do the job.
I prefer DVDStyler which is a free DVD creator program and which gives you full control over nearly all aspects of the creation process.
http://www.dvdstyler.org/en/downloads
Another free program is the SoThink DVD maker. This does a similar job but, if you haven't bought the software it places a green advert screen between each film (or at every bookmark if you have used these). It's not particularly annoying though, otherwise it is free to use with no time restriction apparently and the results are good otherwise.
http://www.sothinkmedia.com/movie-dvd-maker/
Nat