Hyper-V Program Manager
Normally when you are running a virtual machine, we will display a window that exactly matches the size of the guest operating systems display. This is because the guest operating system does not know it is inside of a virtual machine and believes that it is drawing to a physical monitor.
When you are running Windows with Virtual Machine Additions installed under Virtual PC we enable a feature called 'dynamic resizing'. This feature allows you to resize the virtual machine window and have the guest operating system automatically resize to fill the new window. Not everyone likes this feature, and some applications have problems with non-standard resolutions (804 x 826 anyone?), so we provide a couple of options here:
One cool - but little known - trick is that if you have either option (1) or (2) selected you can get the reverse behavior by holding down the control key when you try to resize the virtual machine window.
This feature allows you to resize the virtual machine window and have the guest operating system automatically resize to fill the new window.