Well, you need to play around and see what works best for your situation. Nero WaveEditor can trim your audio and manipulate it to fit where you want. You can make a slide show and add your modified audio to it directly.
You can also make a slide show and export it as a .mpg file and then reinsert it into NV4 to add the audio on a separate track. You can then move the audio file in relation to the video and cut it (if you can figure out how). You can also change the volume of part of the audio if you break the file and just change the properties for that section.
I guess one advantage of putting the audio in when making a slide show, would be you could adjust the duration of certain slides to coincide with the audio.
If you use NV4 to make a DVD movie of the slide show, be aware there are settings under the MORE button that control how the files behave as far as snapping to another file or moving other files when something is added. Or at least it is supposed to allow different types of movement.