When you're in List View you can do it by selecting the "Kind" column (it's generally on the right side by default). It'll sort by file type that way. If you're in Icon View, you can press Command+J (or go to View->Show View Options), check "Keep Arranged By", and then select "Kind". If it's possible in Column View, I don't know of it, since I honestly don't use Column View very often. Oh, and if you don't see the Kind column in List View you can Show View Options and select it from the list of check boxes so that it'll be visible.