ehmm, there is no rollover image in the top image bar. This images are static, or I should put it this way, when you position your mouse over them they do not change. If they been made as rollover they would change to something else or just change colour.
This yahoo bar is simple table like this

[HTML]<table>
<tr>
<td><a href="link_one.html"><img src="first_image"></a></td>
<td><a href="link_two.html"><img src="second_image"></a></td>
</tr>
<tr>
<td><a href="link_one.html">Text link one</a></td>
<td><a href="link_two.html">Text link two</a></td>
</tr>
</table>[/HTML]

Hi
You'r right, I konw they are not RollOver, but in my web page the image is in a diffrent layer from text link, it's my problem!
How can creat a link (image and CSS text link) like links of top of the Yahoo! home page with this diffrent "the image is in a diffrent layer from the text link"?
Thank you for your attention my friend