For minimizing a game the alt+enter has always worked from 9X-Vista. The alt+tab combination in Vista is called the Windows Flip feature.
Windows Flip (ALT+TAB)
Windows Flip is an update to the feature known as ALT+TAB in previous versions of Windows. Windows Flip shows you live thumbnails of your open windows instead of generic icons, making it easier to quickly identify the windows you're looking for. One of the windows displayed will always be your desktop itself, giving you a fast and simple way to minimize all the open windows on your desktop.
ALT+TAB shows a tiny view of every window.
Windows Vista: Features Explained: Windows Aero