If you just empty the posts table for the specific blog (through an admin tool like phpMyAdmin), you will *start over* in regards to posts. No reinstall for that.
Just thinking about what tables one would want to empty to start freash without needing to start from scratch on options settings, etc. It would be:
Then you may want to hit *_categories, and *_links and *_linkcategories if the blogroll needs a new beginning. I guess dropping all the tables for the blog and reinstalling may be easier for most.