If you maximise the window, then the broweser contents should fit to that window, regardless of resultion.
That said, it is possible to obtain a user's screen resultion in javascript, using screen.width and screen.height variables (this depends on the browser supporting this, but as most people are using the latest versions of the different browsers, there shouldn't be any probs). With the size information, one could put a javascript window resize function in overall_header.tpl. Javascript is the only way to get this sort of information about the client environment.
This is a nice little tutorial on javascript size detection:
http://www.phpbuddy.com/article.php?id=8
and this is a nice tutorial on using javascript to resize windows (nice in that it mentions the differences between IE and Netscape/Mozilla):
http://www.javascripter.net/faq/resizing.htm
