Is my MySQL instance irretrievably dead?
Looks like you installed MySQL 5.1 over a 5.0 (or older) installation, without running mysql_upgrade to create new system tables and add columns to existing system tables. –  Bill Karwin 25 mins ago    


It is safe to run mysql_upgrade without disturbing your other databases.

Read http://dev.mysql.com/doc/refman/5.1/en/mysql-upgrade.html for more information