I have fix the float right issue. another problem is that the background image on Li does not show.
#subnavigation {
width: 710px;
height: 22px;
background-color:#FF6600;;
}
#sub_link {
font-family:Arial, Helvetica, sans-serif; font-size:11px; background-color:#FF6600; float:right;}
#sub_link ul {margin:0; padding:0; padding-top:2px; }
#sub_link li {display:inline; padding-left:125px; background: url(../images/arr_subnav.gif) no-repeat 5px 2px; border:solid;}
#sub_link a:link, #sub_link a:visited {
padding: 0px 25px 0px 10px;
color:#ffffff;
background-color:#FF6600;;
text-decoration:none;
border: 0px; float:right;}
#sub_link a:hover {color:#ffcc00; background-color:#FF6600;}
------------------------------------------------
<div id="subnavigation">
<div id="sub_link">
<ul>
<li><a href="#">how we work</a></li>
<li><a href="#">what we do</a></li>
<li><a href="#">who we are</a></li>
<li><a href="#">home</a></li>
</ul>
</div>
</div>