right floated div moving into another div on window resize

[deepuraj]

how can i stop my right floated div from overflowing into another div on it's left?\[code\]<div class="HeaderArea"> <div id="centertopnav"> </div> <div class="srchbox"> </div></div>#centertopnav {margin:0 auto; padding:0; width:780px;}.srchbox { float:right; margin:-20px 290px 0 0 ;}\[/code\]HeaderArea is full body width, centertopnav is centered using margin "0px auto" andsrchbox is floated right but as i resize window, srchbox shifts into the centertopnav..what property do I use to fix this? Overflow? clear? here is screeshot: http://pixholder.com/view.php?id=1160