Oh, that is one of the few things that are still hardcoded rather than being controlled by the stylesheet. There is an explicit <font size=3> in the function forum_make_mail_post() in the file moodle/mod/forum/lib.php. This will all get fixed when Moodle moves to using templates.
I knew it was in there somewhere. That was probably the one file in that directory I didn't check 
THANKS!!!
P.S. The template version will be 2.0 right?