Hover image on top of another image - css

Question

I'm trying to add some hover effect on some images I got.
<div id="horizontal_list">
<div class="grid_3 first overlay">
<a href="#">
<img border="0" alt="first" src="path">
</a>
</div>
<div class="grid_3 overlay">
<a href="#">
<img border="0" alt="first" src="path">
</a>
</div>
</div>
When I hover the div with the overlay class I want another image to hover on top of the imagetag..
I've got the following css:
#horizontal_list{
margin-top: 18px;
height: 330px;
}
.grid_3{
display: inline;
float: left;
margin-left: 10px;
margin-right: 10px;
}
.first{
margin-left: 0px !important;
}
.last{
margin-right: 0px !important;
}
.overlay{
height: 330px;
}
.overlay:hover{
background: url('path') no-repeat;
}

Answer 1

I'm not sure what you mean by 'imagetag' but here is what I think you mean:
What you can do, is adding the second image in your html:
<div id="horizontal_list">
<div class="grid_3 first overlay">
<a href="#">
<img class="first_img" border="0" alt="first" src="path">
<img class="sec_img" border="0" alt="second" src="path">
</a>
</div>
<div class="grid_3 overlay">
<a href="#">
<img class="first_img" border="0" alt="first" src="path">
<img class="sec_img" border="0" alt="second" src="path">
</a>
</div>
</div>
And in your CSS:
.overlay {position: relative;}
.overlay:hover a img.sec_img {display: none;}
.overlay:hover a img.sec_img {
display: block;
position: absolute;
background: url(path) no-repeat;
top: 0;
left: 0;
width: [imgwidth]px;
height: [imgheight]px;
}
Be sure to change [imgwidth] and [imgheight] into the correct dimensions.

Answer 2

HTML
<div class="hoverholder">
<a href="#" class="picone">
<img src="#" alt="" />
</a>
<a href="#" class="pictwo">
<img src="#" alt="" />
</a>
</div>
CSS
.pictwo {display:none;}
.hoverholder:hover .picone{
display:none;
}
.hoverholder:hover .pictwo{
display:block;
}