to resize my map I put an onresize on the body itself which calls a function to recalculate the content div.HTML
<body class="tundra" onresize="onPageResizeHandler()">
        <form id="form1">
            <div id="header">
            </div>
            <div id="leftcolumn" dojotype="dijit.layout.ContentPane">                
            </div>
            <div id="center" dojotype="dijit.layout.ContentPane">
                <div id="map" style="width:1200px; height:600px; border:1px solid #000;"></div>
            </div>
        </form>
    </body>
JS
function onPageResizeHandler() {
    var _header = dojo.marginBox(dojo.byId("header"));    
    var _leftcolumn = dojo.marginBox(dojo.byId("leftcolumn"));    
    var windowsize = getWindowSize();
    _height = windowsize.h - _header.h;
    _width = windowsize.w - _leftcolumn.w;
    var centerbox = dojo.marginBox(dojo.byId("center"), {
        h: _height,
        w: _width
    });
    var leftcolumnbox = dojo.marginBox(dojo.byId("leftcolumn"), {
        h: _height        
    });
    
    var centerbox2 = dojo.marginBox(dojo.byId("center"));
    centerbox2.l = 0;
    centerbox2.t = 0;
 
    dojo.publish("ResizeMap", [centerbox2]);
};
The publish basically calls a function and passes the center div measurements to it
        var mapDiv = dojo.byId(this.map.id);
   dojo.style(mapDiv, {
       left: contentBox.l + "px",
       top: contentBox.t + "px",
       width: contentBox.w + "px",
       height: contentBox.h + "px"
   });
   this.map.resize();
   this.map.reposition();
Looks kind of cumbersome but it works in all browsers without getting into overly complicated CSS if you just want the map to be 100% height and width in a div tag on the page.