div objects and iframe

hi,
the following code produces,
in ie for win and mozilla-based browsers for win/linux/mac,
the div object to be foreground respect to the iframe, because of z-index
css attribute,
but opera browser for win/linux and ie for mac always show the div object in
the
background

<div id="obj1" style="z-index: 2; position: absolute; top: 10px; left:
10px"> ... </div>
<iframe id="myframe" style="z-index: 1; position: absolute; top: 15px; left:
15px"> ... </iframe>

any suggestions?