As of MySQL 4.0.1, FULLTEXT boolean searches can be done using the IN BOOLEAN MODE modifier. At
http://www.mysql.com/doc/en/Fulltext_Search.html there is a list of boolean operators available with MySQL 4.0.1+.
For those using MySQL 3.XX.XX, David Altherr wrote some boolean functions for use with MySQL 3.23.23+. Attached is a ZIP of these functions, which David has released for free under the MIT open source license.