yeah i have the same problem, its when using tables inside iframes the iframe seems to put a 0.5 - 1cm border on either side of the table but its fine untill it needs to vertically scroll then as soon as it scrolls vertically the scroll bar coming in forces it to have to scroll horizontally as well (the scrolling horizontally been the problem).
i've not tried this yet but using something like marginwidth="0" marginheight="0" (if thats right) may work
Whats the problem of making the page fit in the iframe? Always subtract 5 pixels from the width e.g. if the iframe has width=400 your page must be width=395 or 390. Accomplish this using tables. Nothing easier.
actually my post was right, without the 2 pieces of code (MARGINWIDTH="0" MARGINHEIGHT="0" ) added, the iframe by default leaves a margin that is around 1cm big all around the content.