__header
__div class='header-wrapper
____b:section class='header' id='header' maxwidget='1' showaddelement='yes'
b:widget id='Image3' locked='false' title='' type='Image'/
/b:section
____b:section class='header' id='header2' maxwidgets='1' showaddelement='yes'
b:widget id='Image1' locked='false' titles='' type='Image'/
/b:section
____b:section class='header' id='header3' mawidgets='1' showaddelement='yes'
b:widget id='Image2' locked='false' title='' type='Image'/
/b:section
__div style='clear:both;'/
__/div
__/header

I have some questions for you...

1) Your tip works well but I have a problem: I want to have 3 differents images at the top of my blog (as ads images with a different link for each image so) but the first one is shifted upside (actually it's the two others wich are shifted downside I think) and I would like to have them perfectly lined up, how could I do that please?
I am under the "new version" of blogger, my main template is the "original" one and there is my html code (I put "_" at the beginning to make it more readable and "diiv" instead of "div" because your robot doesn't allow me to post this):
---------------------------------------------------------------------
.header {
__float: left;
__width: 33%
__margin: 0px;
}

.header2 {
__float: left;
__width: 33%
}

.header3 {
__float: left;
__width :33%;
}
--------------------------------------------------------------------
__
__
______

______

______

__
__
__
---------------------------------------------------------------------
I tried some stuffs like changing the value of "clear" but the three elements go on each other in a mess, I also tried to add some "top-padding" to the first header but it moves the 3 images and top-padding the other ones don't do anything...

2) I would like these 3 images to be in a "top bar" wich would be as wide as possible (adjusting the screen width and not just shrink in the main page), is it possible?

Of course if somebody has a better idea to solve my both problems in one time it will be perfect (like just putting an html widget but I don't know how to put 3 images with different links in there).
My aim is quite simple: to have a full width top bar on my blog where I can easily put 3 different advertisement pictures...

Thanks again for your terrific website and for your time.

To Add nother Additional Section above you blogger header,

1.Log in to your dashboard--> layout- -> Edit HTML

2.Don't click on "Expand Widget Templates"

3.Scroll down to where you see like this code:

<div id='header-wrapper'>
<b:section class='header' id='header' maxwidgets='1' showaddelement='no'>
<b:widget id='Header1' locked='true' title='YOUR_BLOG_TITLE' type='Header'/>
</b:section>
</div>

4.Now copy below code and paste it just before above code.

<div id='crosscol-wrapper' style='text-align:center'>
<b:section class='crosscol' id='crosscol2' showaddelement='yes'>
<b:widget id='HTML184' locked='false' title='' type='HTML'/>
</b:section>
</div>

Now save your template and you are done.