Ti metto il mio codice:

|code|
/* CSS Document */
body {
background-color: #f5f5f5;
color: #00000;
margin: 0;
padding: 0;
text-align: center;
}
#header {
margin: 1em auto;
border: 1px solid #0F89FF;
min-height: 100px;
height: auto !important;
height: 100px;
width: 90%;
background-color: #ffffff;
}

#button {width: 110px; font-family: 'verdana';}
#button ul {list-style: none; margin: 0; padding: 0; border: none;}
#button li {border-bottom: 0px solid #ffffff; color: white; background-color: #BBCCDD; font-size: 12px; width: 100%;}
#button li a {display: block; padding: 2px 1px 2px 5px; border-left: 10px solid #CEDDEE; background-color: #DCE8F5; color: #6688AC; text-decoration: none; font-size: 12px; width: 100%;}
html>body #button li a {width: auto;}
#button li a:hover {border-left: 10px solid #7CBAFF;}

#menu {
margin: 1em auto;
border: 1px solid #0F89FF;
min-height: 300px;
height: auto !important;
height: 300px;
width: 10%;
background-color: #DCE8F5;
text-align: left;
font-family: Verdana, Geneva, Arial, Helvetica, sans-serif;
font-size: 1em;
style= display:inline;
}
#corpo {
margin: 1em auto;
border: 1px solid #0F89FF;
min-height: 300px;
height: auto !important;
height: 300px;
width: 30%;
background-color: #ffffff;
text-align: left;
font-family: Verdana, Geneva, Arial, Helvetica, sans-serif;
font-size: 1em;
style= display:inline;
}
#corpo p {
margin: 0.5em 1em 0.5em 1em;
}
#corpo p:first-letter {
text-transform: capitalize;
font-weight: bold;
}
#footer {
margin: 1em auto;
border: 1px solid #0F89FF;
min-height: 100px;
height: auto !important;
height: 100px;
width: 90%;
background-color: #ffffff;
}

|\code|

Il problema,è che mi mette in linea i DIV,ma agli estremi della pagina,ma così non deve essere,come vedrai dal foglio CSS