I downloaded the SyncFolders action for Automator... This is running under Leopard. I set up an action to sync two folders and saved it as an Automator application. It runs fine when I run it manually.
I don't now too much about this so I can't tell you HOW to do it, but I know you can assign an automator action to a folder and it will run when the folder is modified. Look around in Automator's help file, I know I've seen something about that in there.