use mysql;
insert into user (host,user,password) values ('localhost', 'пользователь', password('пароль'));

insert into db (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,Create_priv, Drop_priv,Grant_priv,References_priv,Index_priv,Alter_priv) values ('localhost','БД','пользователь','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y');
flush privileges;

или воспользоваться скриптом mysql_setpermission