Nero Conversion to produce DVD

I have successfully produced 25 separate movie and slideshows with nero and I am looking to produce 1 dvd that comprises the 25 separate nero projects.
Cannot seem to get nero to recognise its own images etc…

It appears that I need a way of converting nero disc image files (which can be individually burned to a dvd) to a nero digital file so that i can combine them to make a movie via nero. Assistance would be most appreciated.

Have managed to find a workaround>
Burned each project to re-writeable dvd,
Extracted each VTS-01-01 file from dvd and saved to hard drive (asigning unique no instead of last 01 to each.
Used Nero vision express to make movie from the 25 files created above, set chapters etc and burned to DVD!

You could alternatively used a virtual drive like Daemon Tools to mount the images on so they appear to be a loaded DVD & done the extract that way. Somewhat quicker.