WtFiOpenStack
What the heck is OpenStack?
There are a few OpenStack 101 overview presentations. Here are a couple of nice overviews on the projects from RedHat.
http://rhsummit.files.wordpress.com/2012/05/myers_openstack_overview_iaas1.pdf
http://rhsummit.files.wordpress.com/2012/05/mcloughlin_openstack_arch.pdf