bulk edit posts?

I’ve just switched from MT to WordPress, but rather foolishly imported all my posts (only 76, but I’m lazy), into WP with the default settings enabled.
As a result I only have one category assigned to the posts, and I’d like to change the Author for them too (The author name I used on the MT install is very slightly different from my preferred author name now).
Is there any way to bulk edit current posts so I can just change categories? Is there any way to bulk change the author of the current posts?
I’ve created a local install of WP to test changes on before I update my main site, so I’m happy to break and fix things if required. I would really prefer not to have to manually change the category of each post!
Level of experience with blogging tools in general: Basic
Level of experience with PHP / MySQL etc: total noob.
Cheers