Leopard = 10.5.x
Lion Boot Camp Assistant 4.x and downloads Boot Camp 4.01+ drivers for Windows 7 only
Your question revolves around, "Can I install XP or Vista instead" and you know what? there are lots of and some long threads on the topic.
Why? people refuse to believe they can't have their cake and kick and scream I guess?
Run those old versions in a VM.