While FOREIGN KEY constraints are on the to-do list of features to be added to the MyISAM table handler, they are not yet implemented and may not be for some time. In the meantime you may find InnoDB to be a fine table handler for most purposes, but if you absolutely must move the table to MyISAM then you will lose the ability to enforce foreign keys.
To convert a table to a different table handler, the following syntax can be used:
ALTER TABLE tablename TYPE = MyISAM;
This was first published in October 2004