It was so long ago… I don’t remember if I ran it under 10.5, but probably not. I generally run one OS behind current, so when 5.5.6 came out I was probably running 10.7 or .8.
I ran it (and am running N7 on the same computer) on a 3.2 quad core Mac Pro 3,1 with 16 G RAM.
Chewy