On any system manufactured before 29 April 2005 (Tiger release date) it won't be a problem, as 10.3 was the OS that shipped with the unit.
It *shouldn't* be a problem installing on machines made after then, but you'd be wise to double check if the system was made after the above date as there may be some unsupported tehnologies on the newer hardware; PCI Express for example, was not a technology available when Panther (10.3) was the shipping OS (the PCI Express based G5's started shipping in October 2005), so the final Panther updates may or may not support it.