Tools used:
DVD slideshow GUI
Windows Movie Maker or DubIt

DVD slideshow GUI:
Make your slideshow in DVD slideshow GUI and export as .avs and save the project.

In Ffdshow enable the avisynth video decoder.
Then run start - all programs - ffdshow - makeavis
Load your .avs file and save as .avi.
(The trick is that the avi file calls the ffdshow codec which then calls the avisynth script (normally WMM won't like an avisynth script).)

Windows Movie Maker / DubIt:
The new (small) file with an avi extension can be imported into WMM or DubIt.
Add your music/speak in WMM or DubIt.

Saving from WMM:
Save film file - On the computer - Other options: DV-AVI(PAL or NTSC)
The audio must be split from the video in ex. Super
Load the avi and export as wav(no video) with 48 Hz.

Saving from DubIt(alt.):
Split - Save audio as... wav

DVD slideshow GUI:
Open your old project.
Add music - load your wav.

Now the audio(with music and/or speak) will be in sync with your slideshow and you can export it as you like.

Have fun,