Microsoft says its minimum system requirements for Vista are “a modern processor” (at least 800MHz), 512MB of memory and a graphics processor that is DirectX 9 capable. But anyone who tries to run a Vista system with this hardware will be sorely disappointed.
On the other hand, Novell sells Suse Linux Enterprise Desktop that requires only a 500 MHZ processor and 250MB of memory. You can also find free editions of Linux that can run on a desktop computer with a graphical user interface that is fairly intuitive to use. These desktop versions of Linux will run very well on what they list as a minimum hardware requirement.