If publishing to a Unix server, about 37 is the limit. See
http://support.microsoft.com/default.aspx?scid=kb;en-us;813736 for
details.
If publishing to a Windows server, there is no limit, but the
photogallery may break if there are many images - how many depends on
the server. I have a (private) gallery with 135 photos, which takes
forever to load on broadband.
IMO, 20 images is too many for anyone using dial-up, unless the
thumbnails are very small.
