Most people think that they already know how to make glass in 3D Studio Max, and maybe they do, but there's more to it than just turning down the opacity. That's a technique that may work for background stuff, like an unimportant window or bottle and, frankly, that's what I do in such cases, too. However, when your glass is an important part of the scene, you're gonna need glass that looks and acts like, well, glass! ...and not something 'half invisible.'