Hurrah! - An answer for those struggling with video problems (and this works on Vista and Windows ME, and probably others too)
I too had the same problems as those posting on this thread (although I didn't try out the extra links you've added Andreas - downloading was painfully slow today for some reason)
Instead, I remembered how I got around this problem last time I used AndreaMosaic some years ago in an earlier version.
I downloaded VirtualDub downloadable at http://virtualdub.sourceforge.net/
with main site http://www.virtualdub.org/
and simply loaded up my desired videos and saved them using "Save as AVI..." in the file menu. BE SURE TO CHOOSE A DIFFERENT FILE NAME IN CASE OF PROBLEMS!!
Magically it can change avi files that dont work into ones that do, plus it handles a bunch of other file types, so hopefully you can get all your videos apporved by AndreaMosaic - hurrah!
On the downside, of course creating avi files takes up a lot of room (and for large ones a lot of time), so you might have to keep deleting files once you've finished with them. However, I discovered that you can seemingly abort at any time and the result is still an AndreaMosaic compatible video, so you could even do your conversions via small bits at a time.
If VirtualDub can't open your files (I remember I did have some files not supported once upon a time), there are other programs which can do extra conversions for you. Annoyingly for some videos I had to convert them to a type that VirtualDub could handle, before they then got converted to an AndreaMosaic compatible type. I think I used FlashMPEG conversion software to help there, but can't remember right now, as I don't need it anymore.
Andrea, I hope this little bit of advice helps your community and serves as a token of my appreciation for your software - it should hopefully help me create a great Christmas present for my missus!
Oh, as a final note it would be good to have some sort of summary for what colours are represented by our tile sets. Perhaps a 2 box diagram showing in one box a palette of colours on one side and in the other box some representation of tiles matching those colours. That way we can see what colour areas our tile sets are weak in, and then it is easy to start photographing more blue seas, green grasses, yellow buttercups etc to create better mosaics with less duplication.
As a rough illustratiopn perhaps something like:
Pal. --- Tiles###
Assuming that dark pink on the right hand box represents strong representation within the tile set, I could see I have plenty of light pinkish types of tiles, but not so many blueish ones. I could then think that extracting pictures from a yachting trip video would probably be a better idea than yet another video of my baby girl strutting around in her pink outfits. Would save a lot of time by making me more efficient!