I've long usod the patch for putting arbitrary wikitext into the side bar, but but according to the manual it won't work in the latest version of mediawiki. I really don't like not to update, but neither do I want to lose this possoibility. What is there to do?
http://www.mediawiki.org/wiki/Manual:Interface/Sidebar#Allow_wiki_markup_.28PHP.29
Allow wiki markup (PHP)
Many people on support desk have been asking about how to put arbitrary wikitext into the side bar. You can hack your skins/Monobook.php file (if you're using monobook) and replace the following section of code. (Note that this patch doesn't work for the new MediaWiki 1.13.2)
/BP 8^)>