How can I make WP Forum server span the whole page?

Hi - I have WP Forum Server installed on http://www.studentconnect.co.uk and on http://www.wagercentre.com. On Wagercentre.com I was able to make the forum span the entire page, but on Student Connect, even copying across the entire css it remains stubbornly in the middle of the page.

I want the forum to align on the left against the primary sidebar and to span the rest of the page. Here is how it looks now http://www.studentconnect.co.uk/wordpress/forums/

This is a problem I seem to come across a lot with Wordpress. It's a pity there is no plugin that allows simple manipulation of the margins on single pages without messing with CSS. Sometimes it seems to code is so deeply embedded it is a major task (for me anyway) to find the lines of CSS that affect the formatting of plugins.

Please help!

Regards, Paul