about html/css, centering div?

[crossroad]

I want to center my div so that it will appear at the center of any browser. How do i do that? text-align:center and margin:0 auto is not working.

It goes like this right?
for the html
<div id="container">
<div id="first"> </div>
<div id="second"></div>
</div>


css
#container {
width:800px;
float:left;
background-color:blue;
margin: 0 auto
}

again...margin:0 auto or text-align:center is not working, can someone please direct me to any tutorial or can give me some advice. I've been searching for one whole day and still no luck.
I just want that container to appear at the center. Thanks in advance

 

[Joshua J]

try using

#container {
width:800px;
float:left;
background-color:blue;
margin-left: auto; margin-right: auto;
}