rpm -e mysql-server yum install mysql-server
should accomplish what you want.
Only think I'd add to this is that removing the rpm doesn't remove any of the existing db files in /var/lib/mysql/ so if something is hosed in them, it will remain hosed on new install. If you haven't put anything in the db yet, I'd nuke the files in /var/lib/mysql/ before the yum install mysql-server command.
-- Jim Perrin System Architect - UIT Ft Gordon & US Army Signal Center