Echoing the previous comment somewhat-- what about hadoop do you want to learn?

If you want to get practice with map-reduce patterns themselves, but not spend much time worrying about the ops associated with setting up hadoop clusters, you can play with Elastic-Map-Reduce (EMR) on AWS.

There is even a great python-based open source tool called mrjob (http://packages.python.org/mrjob/index.html) made by some folks at Yelp that makes using EMR really easy. There are a bunch of great tutorials already out there.