Wordpress ascending/descending order of posts/sub-categories

On our (Wordpress) site we categorise our posts. However due to Wordpress default those posts are listed in reverse order, with latest posts at the bottom and oldest posts at the top. We'd like it to be the other way round with latest posts at the top and older posts at the bottom

I’ve installed a few plugins which should in theory fix the issue but they don’t appear to work. I'm looking for a Wordpress expert to fix this.

Our site runs on Wordpress 3.0.5 and the plugins I've tried are:

Ascending Posts Plugin Version 1.3 by Fly Plugins
AVH Extended Categories Widgets Version 3.6.7 by Peter van der Does
Category Order Version 1.0.3 by Wessley Roche

Thanks
Arthur