I have installed Joomla (a Mambo based CMS) and Simplemachines with the Joomla-SMF Bridge and it works great. I have both of these working off seperate databases. Seeing how as versions have updated, I’m using a different, though similar, CMS than you are and things have changed since you posted, I’m not sure that any of this applies. Try updating to the newer version of the software. Possibly even consider switching to Joomla CMS, since I know that it works personally, and it was easy and took all of 5 minutes.
Hope this helps!