I have a Google Maps app that takes up most of the page. However, I need to reserve the top-most strip of space for a menu bar. How can make the map div automatically fill
I recommend you to try jquery-layout plugin. You will see a bunch of demos and examples on the link.
I don't know if you are familiar with the concepts of JQuery or some other Javascript helper framework, like Prototype.js or Mootools but it's a vital idea to use one of them. They are hide most browser-related tricks from the programmer and they have a number of useful extension for UI, DOM manipulation, etc.