Set your server to ‘adventure’ mode, and they can’t touch the landscape. That makes construction difficult, but that’ll keep your custom map intact.
As for pulleys and other fun toys, try Bukkit server. They’ve got some crazy addons like nukes (much larger destruction radius than TNT) and even quarrying drills. I’ve played on a Bukkit server, and it’s a lot of fun.
I want to try Bukkit, but my version is 1.7.2... Will have to wait awhile for the good mods to get updated :p