Background Noise:
I've installed Leopard on three machines, the MacBook with 2Gb of RAM, the G5 with 3.5Gb and the G4 MacMini with only 512Mb! The MacMini appears to be running fine. The fan increases to a high flow when playing video, but the 'Mini is otherwise as happy as it was under 10.4.10. The 2Gb is I think a guide for getting the best out of Leopard, rather than an absolute minimum.
Applemacster