I would redo your NTSC Sequence to PAL. As you have 4:3 & 16:9 footage, you will need to decide which treatment you will use for those. If you will be letting th 4:3 Pillarbox (black bars on the sides of a 16:9 Frame), then set up that PAL Seqence for 16:9. If you are going to place your 16:9 footage into a 4:3 Frame, and either Letterbox it, or Scale and crop to fit, then set up that PAL Sequence for 4:3.
Depending on the amount of animation in your NTSC "slideshow," you might test converting it to PAL, and see how smoothly everything plays. That might get you adequate footage, without having to redo anything - just a simple conversion in one of many conversion programs (many free).
BTW - I have converted some PAL to NTSC (the opposite direction to what you need) with the older DigitalMedia Converter 2.7 (Deskshare), and with low-motion footage, it looks pretty good. Only you can be the ultimate judge of the converted footage. Note: Deskshare has updated that program, and I have not used the newer versions, but would guess that if anything, the conversions are as good, or perhaps better, than my older version. Again, many options, and many are free, however YMMV.
Thanks for the answer!
I don't want to use any software to convert the whole slideshow-movie.
I think the best way is to use a 16:9 sequense and get black bars on the sides. I downscaled the pictures to 864x576 and it seems good in the project. What do you think about it?
Can you explain more about how to Letterbox? Do I have to crop my images?
The other movies on this DVD
The first movie is 1920x1088 (Source), edited, saved as a lossless video codec (1920x1080) then resized to 704x576 and added borders(8,0,8,0) when encoded.
Movie 2 and 3 is DV 720x576 (Source) and I choose 4:3 when encoded.
When a Sequence's Frame Size is different, than the pixel x pixel dimensions of the Source Files, then cropping, Letterboxing, or Pillarboxing will be a natural occurance, depending on how you treat that Source Footage. You should make the aesthetic decision on how you treat it.