3120 Add column to Wordpress theme

I'm developing a site running WordPress, using a customised four-column theme. I'd like to add a fifth column to the left of my page. Take a look at bathradar.co.uk. See the sidepanel on the right, with the search box and the two ads? I basically want one of those in the same position, only on the left hand side of the page. The content of this sidepanel won't be posts as such - only ads. Any questions please ask!