You need 5.1 for any sort of partitioning that I know of. It's currently in a final RC stage so it's mostly stable. Otherwise, I would wait until their official release. http://dev.mysql.com/downloads/mysql/5.1.html
I haven't jumped into it too much, but here's the partitioning section from mysql: http://dev.mysql.com/doc/refman/5.1/en/partitioning.html.