Some characters changed to "Squares"

Hey All,

This one has got me. I'm sure it's a character encoding thing but I can't track it down.

I have an issue that any "'" (apostrophe) or various other characters show up as little squares in IE7 or a questionmark type icon in Mozilla.

This happened after a server rebuild and the data is the same and fine.

Each webpage has the following tags:

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">

I've also forced the default apache2 charset to ISO-8859-1 as well as the PHP charset to ISO-8859-1.

The only thing I haven't done yet is change the Linux charset. It's a CentOS 4.4 install that is default en_US.UTF-8.

If I view the source of the page in IE7 I see the apostrophe so it seems that the actual character is coming across fine.

Please someone tell me what silly little thing I'm missing?

Thanks,
Serge.