Har du prøvet med height="100%" ?
Here are a few more commands that you can use in order to alter the frames on your page. Each is fairly self-explanatory and doesn't really require an example. I've used them all just to make sure they work. Just stick the command, with whatever setting you want, into the IFRAME command to see it work.
HEIGHT="--": This acts just like the height command in terms of an image (see here). It defines the frame's height, in pixels or percentage.
WIDTH="--": Ditto this one in terms of frame width.
MARGINWIDTH="--": This sets the margin width in either pixels or percentage.
MARGINHEIGHT="--": Ditto, but on height.
SCROLLING="--": If the information inside the frame is too long to display, then a scroll bar will appear. You can stop it by adding this command set to "no."
ALIGN="--": This works like the align command in terms of images (see here). It denotes where text will appear when surrounding the frame.
NORESIZE: Add this, and the user will not be able to resize your frame.