GlenS: Maybe you could try changing the forum software and database to use UTF-8? It really is the standard encoding that most new software in the world uses if it cares about special characters, so if we can use UTF-8 on this forum instead of more limited ISO-8859-1 then it should fix a lot of issues. I still have not figured out how to post Chloe's name with two dots over the e in a way that shows up properly. While there are workarounds for some browsers like Tom mentioned, it's annoying and needless to force users to switch browsers and employ those workarounds.
For the forum software, there is probably some administrator control panel where you can find a "charset" or "character set" setting and change it to "UTF-8". Looking through the source code of SMF, it really seems like it does support using UTF-8.
I'd recommend that you also make sure that your database is configured to use UTF-8. If you are using MySQL,
remember to specify utf8mb4, not just utf8.
--David