Hyper-V Program Manager
When you create a new virtual machine - you will be prompted to select which operating system you are going to install. Now - a number of people wonder why we ask for this information - and how we decide on what operating system to display by default.
The answer to the first question is that we use this information to suggest appropriate default values for the memory and virtual hard disk size. Once you have completed the new virtual machine wizard we completely forget about this selection - and you can now install any operating system you want.
As for how we decide the default operating system to select - we actually inspect the name that you put in for your new virtual machine and attempt to 'guess' the operating system that you are planning to install. So calling a virtual machines "Ben's new experience" will result in us selecting Windows XP by default (because the name has 'XP' in it).