var navToolbar;

function createNavToolbar(map){
    navToolbar = new esri.toolbars.Navigation(map);
    dojo.connect(navToolbar, "onExtentHistoryChange", extentHistoryChangeHandler);                      
    extentHistoryChangeHandler();
}

function extentHistoryChangeHandler() 
{
    var oPrev = dojo.byId("ZoomPrev");
    var oNext = dojo.byId("ZoomNext");    

    if (navToolbar.isFirstExtent())
    {
        oPrev.setAttribute("currentstyle","ZoomPrevStatic Tool");
        oPrev.className = "ZoomPrevStatic Tool";
    }
    else
    {
        oPrev.setAttribute("currentstyle","ZoomPrevActive Tool");
        oPrev.className = "ZoomPrevActive Tool";    
    }
    
    if (navToolbar.isLastExtent())
    {
        oNext.setAttribute("currentstyle","ZoomNextStatic Tool");
        oNext.className = "ZoomNextStatic Tool";
    }
    else
    {
        oNext.setAttribute("currentstyle","ZoomNextActive Tool");
        oNext.className = "ZoomNextActive Tool";    
    }        
}