Hammerheads (or stall turns) ARE a lot of fun. Not sure they teach you all that much about rudder, but they get you use to using the left stick at least.

I would make one change to SHenion's technique though. On virtually every trainer, and most sport planes it's necessary to use full throttle to get the aircraft to "turn".

The technique would be; full speed (or close to) level run, pull up to vertical and chop throttle to idle, as plane looses almost all airspeed (but before it does) give full throttle while adding full left rudder at the same time. (I say full left because engine torque and prop wash will help pull the plane around.)

The goal is to get the aircraft to do a 180 turn on it's wingtip. ie, the left wingtip stays in one spot while the rest of the plane swings around it.
Dennis-