this steps work in squeeze as well (02.2012):

• redmine.org/...HowTo_Install_Redmine_on_Debian_Wheezywith_MySQL_and_Apache2-Passenger

• Howto install plugins: http://www.redmine.org/projects/redmine/wiki/Plugins
• List of all Plugins: http://www.redmine.org/projects/redmine/wiki/Plugin_List

embed HTML:

{{html(<br/><br/>)}}

inject an external JS or CSS file:

{{js_url('http://www.domain.com/js/widget.js')}}

{{css_url('http://www.domain.com/css/styles.ui.css')}}

• install this: https://github.com/mexitek/redmine_wiki_html_util/blob/master/README.textile
• info: http://www.arlocarreon.com/blog/redmine/redmine-wiki-html-utility/