There's no syncing function, but you can get by with exporting/importing Projects from one machine to another and deleting the old copies of the Projects. Just make sure you are using referenced Masters or the Project files sizes will be absurd
This approach is a lot more feasible with Aperture 2.0 - they added the ability to force the reconnection of referenced masters. When you move projects between machines like this, you'll need to reconnect the masters to their new location on disk. The gotcha with the 1.5.X release of Aperture was that it wouldn't always reconnect - it often found "differences" between the masters when none existed.
In 2.0, you can hold down the option key and force the reconnection to the files that you know
are the same.