object tag :how to access/manipulate ?

Hi,

I have an object tag to display small html files when mouse goes over a
link.

<div id="pop">
<a name="close" onclick="(here the function to hide the pop
div)">Close&nbsp;[X]</a>&nbsp;<br />
<object id="obj" type="text/html" data="noFileNow.htm" height="200"
width="300"></object>
</div>

The problem is that when I try to change the html file displayed with
the following script :

document.getElementById('obj').data=http://www.myserver.net/myfile.htm;

The code is not working with IE6 and in FF it needs to go two times
onmouseover to display correctly.

Can you help me or indiacte me a page to understand how to manipulate
object tags with javascript ?

You may see my test code here (put your mouse over the test1 to test3
links) :
http:||arthur.opendns.be|mariavaltorta|test.shtm (please replace | by /)

TIA