Hi Zach,
there are a few great plugins around for cleaning up the database (post revisions etc.)
WP-optimize will do exactly what you are looking for:
http://wordpress.org/extend/plugins/wp-optimize/
the WP database is split into several tables which holds your website data. All your posts are saved in "wp_posts"
as far as I remember you can backup specific tables with this plugin:
http://wordpress.org/extend/plugins/wp-db-backup/
hope that helps :)