Todd Lipcon gives a brief introduction to HBase, Hadoop's database. Todd goes on to explain HBase usage scenarios, how HBase compare to an RDBMS, and how HBase complements Hadoop.
http://player.vimeo.com/video/14068552
Introduction to HBase (Ch1) - Todd Lipcon from Cloudera on Vimeo.
Also there is a nice beginners article by Jim Wilson
