I followed the excellent instructions at http://en.support.wordpress.com/images/gallery/ to create a gallery but I had a lot of trouble figuring out how to a) add an image to pre-existing gallery without re-uploading all of them, and then I also wanted a separate post for each image so I could tag and categorize them. I did figure it out (with the help of a friend) and I documented it so I wouldn't forget how to do it next time! Might help someone out so here's a link to the tutorial:
At the time of this writing my instructions were created using WordPress 3.0.4.
The blog I need help with is nosillacast.wordpress.com.