Re:Integration
I noticed that tiki is using the pear::DB module for database access. I am not able to check right now what tiki used for authentication, it could be a pear module. What this means is that you could probably call the pear modules yourself, as the use of the classes is fairly standard, due to pear. You would need to find out the how IBP (don't know anything about it) is doing it's signon/db though, as you are probably wanting to use their user list, right?
Another thought. Does IPB use a cookie to store users? Just wondering if you could use that cookie info to pass the signon info to tiki.