Ubuntu Enterprise Cloud (UEC) uses OpenStack by default, which makes it easy to add, install, and maintain your cloud computing environment. An alternative to UEC is Eucalyptus (which was UEC before Ubuntu changed it to OpenStack), which is easy to set up and install.
To install OpenStack, just install Ubuntu Server, and select 'Install Ubuntu Enterprise Cloud,' and follow the prompts to install the cloud manager software. Once you've got the cloud controller installed, it'll walk you through installing the cloud nodes, and then you just make API calls to the cloud controller who will call the individual cloud nodes to create the instances that you request.
Installing Eucalyptus is a bit more time consuming than installing OpenStack (as it's not automated from the Ubuntu Server install), but, it will provide you the same basic functionality as OpenStack will once completed.