build quality?
Doesn't the SD400 have breaky lcd? Or was that the SD200?
Upgraded my wife's canon S100 to a Z750. Thought the Z750 would be larger/feel cheaper but it is the exact same size as the S100 but has a much bigger LCD and pretty good feel to it. So far the wife is amazed and loves it.
The SD400 is smaller than the Z750 so if size is what you want, go with that.
there are sample picts for both cameras everywhere, including this forum.
Here's a few more for the z750
http://www.rudedogmedia.com/rudedogphoto/
Be aware the MPEG4 is a dual edged sword. Smaller files but Casio claims minimum computer for playback is 2Ghz P4, and I believe them. A friend with a 1.8 ghz computer has problemns with the sound synching with the video on my Z750 videos....
To me both camera's look great, I don't think you can go wrong. If you need the MPEG4 than the Z750, small size, like canons the SD400/500.