If you are using vendor software like most people (ex: phpBB, wordpress blog) then you probably have different databases set up for those to run on. Also, they may be set up to run on different DBMS (database management system) For example, phpBB could be running on mySQL and wordpress could be running on postgresql.
The problem with this is that these vendor projects are setup so that they are no aware of each other at all. Sharing data is not easy to do without delving into the internals of each program and trying to merge them together.
If these are all systems built by your company, then it -might- be easier to do in that you know how the systems work. Really though, if they were not built with working together in mind then the only advantage is that you know the individual systems better than vendor software. This is good, but can still be pretty unhelpful.
A lot of how they function would probably have to be reworked because they have their own users (this is probably the main thing) and the code itself was written to work with only that data and logic. (if a new blog is posted.. do blog stuff. It doesn't have code to do forum stuff).
Really.. I could go on and on, but I think the simplest path here is to sit down with you dev folks and talk to them. I am sure they will talk to you as much as you can stand
