Microsoft have launched a new site Windows Vista Business Test Drive to allow users to use the latest operating system without having to install it on a machine. Its ready to go. If your not sure what your doing, then it has videos and sceneries to help you.
http://www.windowsvistatestdrive.com/
This is great if you need to demo the application without powerful enough hardware as well, all you need is a Internet connection. Don’t expected any aero effect as its done over Terminal Services.