AFAIK, "window.resizeTo(width, height);" is fairly cross-browser (it works for me in IE, NN, and FF at least).
Making this happen onclick would not be a good idea, IMHO - it would seriously annoy a lot of users every time they clicked (especially if they kept resizing their windows back to how they like it only to be resized by your code again... you know - personal preference, not like "all your windows are belong to us").
Dan
The answers you get are only as good as the information you give!