My wife's powerbook is a 1.5 with 1.25 of ram and a recently upgraded 160gb hdd. I did a fresh install of Leopard and it works amazingly well. It also seems to have cured its "narcolepsy."
I highly recommend it.
@jtus - your friend only has a measly 512mb of ram, that's why Leopard runs so slow. Even if you are determined to go back to Tiger, you should get more ram (it is very cheap). But that would likely solve your performance problems with Leopard.