As a start point I took the last public available version of joomlawiki: http://www.joomlawiki.org/
As it uses mediawiki version that is 2 years old I updated to the last available version of mediawiki 1.12.0
There are still some problems - mainly comming from database changes, but that is going to change.
I also made the login in mediawiki possible (if we have a user in joomla's database) http://www.mediawiki.org/wiki/Extension:AuthJoomla/ja
That is all good, but I don't want to have mediawiki in an iframe.
so from here on my idea is to hack the mediawiki software and make it extension of joomla 1.5 and not a standalone installation.
We could use for example the joomla's user table instead of the mediawiki one.
We also should work on the view and so on. I will be very happy on suggestions and ideas!
Greetings!
Daniel
P.S. I registered the project on joomlacode: http://joomlacode.org/gf/project/jowiki/ So anyone interested in developing - please join the project
