I finally got it fixed - it was definitely my Adobe Helvetica.
Even though FontDoctor X said it was fine, if I turned it on in Suitcase (green bullet) and then opened Safari, it turned into weird characters. If I turned it off in Suitcase and then opened Safari, the page would look fine & if I looked in suitcase, I could see that Safari had actually launched Helvetica (yellow diamond). Definitely some kind of conflicting information.
So I started trying different combinations of Helvetica from each of our computers and our old backup files & finally got a package that FontDoctor said was ok, didn't conflict with the system fonts, and opened up correctly in Safari. What a pain!!!
I had even previously had FontDoctor build me a complete new library - ditched extra sizes, included opentype, bitmap and postscrip fonts, excluded multiple master and true type fonts - just to make sure I had a nice clean package. But now that I think of it, I told it to skip the system fonts, so maybe that's the problem - maybe the system fonts have to be included when you organize the fonts just to remove any possible conflicts. If I have time, I guess I'll try it again but so far so good.