List posts in specific category (including child categories)

I cannot for the life of me work out how to do this. I have a category called weblog, and subcategories. These subcategories will increase over time. I would like to list the last 5 posts found in “weblog” or any of its subcategories.
I’ve searched and searched – I’ve found a plugin that shows just one category, a plugin that makes you specify the categories… Can anyone help?