To follow up on Limnos' excellent advice, original full install Leopard disks look like this:
and will NOT have "updater" printed on them.
Leopard retail install disks came on both CD and DVDs, but DVD readers were optional in some G4s. Make sure you know what kind of optical disk your iMac can handle. The serial number sticker should show what optical drive shipped with the computer. Original Leopard CD disk sets are rare and can cost more the the current market value of several old Macs combined.
i want to download OSX 10.5 PPC
Very ill-advised. Do not attempt to download any macOS system not offered by Apple. Most don't work and you can't get your money back, every one is pirated, and too many of those downloads come with little somethihgn "extra"—a severe adware infection.
Avoid any gray system install/restore disks:
They are too often keyed to only work on one PowerPC model.