Here’s how I did it:
mysqldump -uroot -p rubyrescue | sed 's#rubyrescue.com#rubyrescue.com/blog#g' > temp.sql mysql -uroot -p rubyrescue < temp.sql
The only other item was dealing with permalinks. The error handler for lighttpd was set to look for index.php in the root. I had to change that to look for it in /blog.