Unfortunately, Leopard's Sync Services don't support CalDAV servers. (This came as a surprise to a lot of developers, including us.)
Fortunately, we're building direct
OmniFocus-to-OmniFocus synchronization into version 1.1. For the situation you describe, this is a lot more useful anyway: it synchronizes all your data (including attachments, project and context relationships, etc.) rather than just the limited amount of task information that is supported by CalDAV.