The Inquirer reports Microsoft has confirmed that Windows 7 touchscreen devices will work with the Metro user interface of Windows 8, although it may not be perfect:
Microsoft outlines what it means by Windows 7 touchscreens working by saying, "This means that touch drivers continue to load, and you can perform the basic touch interactions in Windows 8 with a reasonable degree of success." The firm says 'reasonable success' means that windows might not align perfectly when dragged by fingers or interpreting gestures such as swiping and pinch-to-zoom.
According to Microsoft, Windows 8 will understand the user's intentions in its touchscreen behaviour. Microsoft claims this will help the operating system use 'sloppy' user touch-based input, something that isn't a problem with keyboards and mice because they produce very specific inputs - a particular keypress or a right click on a particular pixel.