Yes. Ive done it myself... Just make sure you can boot from a CD (turn off open firmware password through your leopard install disk first) also totally wipe the HD you want to use and make sure you dont format it as 'journaled' (if you want to install osx then partition the disk first and just format the osx partition as jornaled like normal
Power Mac G5 (11,2) 2.3 GHz 8 GB Dual boot YDL 6.1 / MACOSX 10.5.6