Nope. I have tested the updated header format with Opera, IE, Konquerer, and Mozilla. All seem fine.
I do have one thought. Are you using an older version of IE? Some 5.x releases fail to properly parse IFRAMES in certain situations. Forget about 4.x, it is hit or miss at most sites.
Even at low resolutions, the IFRAME should be there, though it will probably look horrible.