Frames can vary in size from browser to browser. Although you can measure the height of a frame, setting it accurately to a desired and exact size is virtually impossible. MSIE is marginally better at this than Netscape.
Height and width control of frames in Netscape is nothing less than a lottery. There are all kinds of platform dependent weirdness that crop up and you may find yourself doing a browser sniff and building in corrective document.writes() that fixes the frame sizes on the fly.
Note that there is no width property to be able to measure the frame width value.