This is for problem 1)
You can reposition the container div to suite your tastes. You should have a doctype in all pages. Your image has a slight border that should be removed:
Code:
<!DOCTYPE html>
<html>
<head>
<title>index</title>
<base href="http://exogenese.altervista.org">
<style>
body
{
margin: 0px;
padding: 0px;
//JUST TO SHOW YOU WHERE THINGS ARE REMOVE COMMENTS FOR FINAL
//background-color: #000;
}
#container
{
position:relative;
width: 960px;
margin: auto;
}
#lang
{
position:absolute;
top: 250px;
left: 730px;
}
</style>
</head>
<body>
<div id="container" >
<img src="images/bg0.jpg" width="960px"><!-- THE SAME AS YOUR CONTAINER WIDTH -->
<div id="lang">
<img src="images/fr.gif" alt="drapeau 1" width=200px height=100px><br>
<img src="images/uk.jpg" alt="drapeau 2" width=200px height=100px>
</div>
</div>
</body>
</html>
For problem 2: set the width to something smaller in the css file:
Code:
.c {
width: 1500px ; // TRY 960PX AND GO FROM THERE
margin-left: auto ;
margin-right: auto ;
}