You can download the current version of Aperture and try it for free for 30 days. This is a full, complete working edition of the application with no limitations.
Even better, the current demo version available is the same V. 1.5.2 that registered users have access to. Another thing to keep in mind... if you are a developer, you can grab this demo version, then get the Aperture Export SDK from the Apple Developer Connection site and play with writing an Aperture plug-in for the application.
No matter how you want to experiment, the Aperture demo is worth trying if you're interested in professional level photo workflow.