How high would you make the content of a page that must fit the screen without the user having to scroll?

Also, more a javascript question tho, anyone know if it's possible to change the height of a <div> automatically to fit this area depending on the users screen resolution?

For an 800x600 screen resolution, the max height to avoid scrolling would be 560-570px .
You don't have to stretch a div's height with javascript, it can be accomplished thru CSS.