According to Pinnacle sites, they recommend this method:

If you wish to combine two projects into a single project, please do the following:

1. Complete each project and render it as either an .mpg or an .avi file. (Example: test1.mpg and test2.mpg)

2. Open Studio and begin a new project. Browse your computer and locate the first project (Test1.mpg) you wish to include in your final project. Drag the first project you wish to combine onto the Timeline. Do the same with the second project (Test2.mpg).

3. Add any titles or transitions or menus that you wish at this time.

4. Save the project by giving it a new name (Example: Final.stu).

5. Click on Make and output your project in your desired format.

My question is doesnt this reduce the video quality when we re-render to DVD? or does it simply create the vob files and write it as it is without any loss?

Your response is much appreciated.