Ok, I got the bridge working, found a fix for xcache and NOW all seems to be fine, lol. I'll post a link when I get a bit further, or get the link from my sig and try it now, lol. Anywho. I do believe there is a brdge for SMF and joomla. Lots of options to that I can see.
EDIT: Works with 2.1
Things that work:
who's online
topics display on Joomla from SMF
user Pm on Joomla
login to both from joomla
Something still need to be configured a bit but most is up and running.