css3 div alignment question

[Ruckus]

ok got a header with the first div as

#header_content{
	color: #fff;
	width:980px;
	height:45px;
	text-align: left;
	font-size:20px;
	margin: 0 auto;
}

within that div is other divs with content(basically logo and menu text)
i left it centered page with margin 0 auto
I want to add a 2nd div floating right of that div to hold social media icons. How do i accomplish this?
I tried

#header_social{
	width:180px;
	height:45px;
	float:right;
}

but it floats bottom right of the other div not next to it