Movie size

I am starting to make a new second web and have a few questions; My last web was less than 550x400 and when viewed on a 19" monitor one can see the bottom missing, even though I have it set @ 100% x 100% and also have the borderless javascripts in my HTML. I thought was because the fact the movie was only some 330 height. I just started making a new movie, thought it would have to be 100x100/550x400 and when I went to preview it there were larger margins around on each side than on the bottoms. Will this all go away when I publish and place inside a Javascript borderless HTML? I don’t want that same problem to happen that happens when you view it on a 19" monitor, where the bottom is short and doesn’t take up entire screen. Looks bad. Input?

I don’t know… I work projects at only two sizes.
600/800, and 1200/1600… Sometimes I’ll do a 600/600, or an odd 400/400.

really though I never try out those borderless windows and such…