Installing OS X 10.5

I've wasted too much time chasing down teaser ads about Leopard downloads. I need some solid advice please. I am recycling my old PowerPC G4 to act as a home server. I've erased one of the drives to make way for a fresh install of Leopard. Can someone please direct me to a reasonably priced download of fresh install software? The software I downloaded from Softonic after wading through the pitches for other software turned out to be an update to 10.5.6 and obviously won't work. Any help?

Thanks a bunch,

dmingo