There are actually two steps to building a highly available virtual machine from scratch. The first is to create the virtual machine. The second is creating a cluster resource that enables the cluster service to control the virtual machine. Both the GUI and PowerShell can be used for this purpose.
Right-click on the Roles node, navigate to Virtual Machines, and click on New Virtual Machine. This will present a dialog asking you which node you'd like to deploy the new guest on. Highlight one and click on OK. This will start the virtual machine creation wizard.