Don't worry acrylian. I perfectly understood what you suggested. sbillard actually explained how to do this (before I had a look at the user guide) with the admin toolbox, with an option I didn't even know (hence the simplicity of the approach). So that my thanks really goes to all of you!
Right now, I'm starting to play with dynamics albums, which I really love! Instead of using tags, I found that using any other field (e.g. "State", which is happily ambiguous for me) is much better: 1) it does not add anything in the template while looking at a picture (tags are displayed below the picture), and 2) it does not mess with the tag system, which is a good thing afterall.
However, I was wondering if there was any way to use an EXIF field for this, hard-coded directly in the picture (I guess that additional fields coded in zenphoto --state, country, etc.-- are just stored in the data base) so that the picture itself would tell if it's featured or not? But in this case, I wonder if zenphoto is able to search in EXIF fields. It doesn't seem possible from the search box (no EXIF check box), but using for example "state", I ended up with a dynamic album with the search "words=bli&searchfields=64". Is there any hope in the 64 search fields for EXIF fields?
Thx again! I'm using zenphoto for years, but I'm just starting to really play with it, and it's just a great tool

M