Hi Dave!
Right now there's not much you can do with treating partitions as tables, but I think that we intend to introduce such capabilities in future - whether this will make it into 5.1, I can't really say right now.
For now, you can do ALTER TABLE ... ADD PARTITION, ALTER TABLE ... DROP PARTITION, and ALTER TABLE ... REORGANIZE PARTITION, which may help in some situations.
I believe that we'll also be introducing WHERE-clause optimisations that will speed up queries in the manner that you describe (don't scan partitions whose ranges don't match the WHERE).
Mikael might be able to tell you more.
cheers
jon.
Jon Stephens
MySQL Documentation Team @ Oracle
MySQL Dev Zone
MySQL Server Documentation
Oracle