After fighting several days without success I decided to change the purpose of !jowiki. Mediawiki is great. As I see - it will stay great, but will not be integrated with joomla - at least not from me. Integration in an iframe seems easy ( I got that - as the guys from http://www.joomlawiki.org/ ), but completely integrating in it in joomla was not possible for me. Andrew from http://www.r5gordini.co.uk/ have somehow managed to integrate mediawiki with joomla1.0, but I was unable to get his script working for me with joomla 1.5.
However, I was really inspired from a web page with scripts for the shortest wiki in the word :) That is when I realised - the concept behind a wiki is not complicated. It depends on what you want. So, I've changed my mind and started working on a wiki extension for joomla. It will be very basic, but it will do the job. And then day after day, line after line it will become better and better! If you wish to help, you are welcome!