Apple today actually released Java 6 for Leopard! Not too bad, since Sun shipped it in Dec 2006...
Looks like it's only for 64-bit Intel HW - PPC and even 32-bit early Intel Macs are out of luck!?!
SoyLatte project mentioned here earlier manages to deliver open source Java 6 for both Tiger and Leopard, and both 32/64 bit Intel! If they manage to add graphics/sound support it will be interesting!