--- Comment #4 from Michal Marek <mmarek@novell.com>  2007-06-18 06:49:02 MST ---
# rcmysql stop
# mkdir /srv/blah
# mv /var/lib/mysql/* /srv/blah/
# vim /etc/my.cnf # added 'datadir = /srv/blah' to section '[mysqld]'
# grep datadir /etc/my.cnf
datadir = /srv/blah
# rcmysql start
Starting service MySQL                                               done
# ls /var/lib/mysql/
tmp  mysql.sock  mysqld.log  mysqld.pid
# ls /srv/blah/
ib_logfile0  ib_logfile1  ibdata1  mysql  mysqld.log  test  update-stamp-5.0

This worked for me both with 5.0.26 from SP1 and 5.0.18 from GA (just there the
temp dir was called 'tmp' instead of '.tmp', so I had to move it back).