Yes. Guess what? I even have some old code which does it (combined with a lot more). It's not quite as trivial as you might think. Well it is in theory. But in practice the existing code still assumes a fixed 800x600 screensize in a few places. For example, the book GUI is always centered to an 800x600 screen regardless of the actual screensize.

On top of that some larger graphics (such as the book and NPC GUIs and various dialogs) are as big as they are and won't fit on a very low res screen.

This is also true of the map as a whole. This gets round it by being scalable, and I extended that to the whole screen (so any x by y res works fine). Problem is this is slow as hell currently (very CPU intensive).

But bearing in mind you may lose the edges of big gfx, allowing <800x600 is not too hard.