RadMenu can work in a static mode. To make RadMenu static you should apply the following
        CSS style to the menu object:
    
<style type="text/css" >
.RadMenu_Fixed
{
	position:fixed !important;
}
* html .RadMenu_Fixed  /*required for IE6*/
{
	position:relative !important;
	top:expression(eval(document.documentElement.scrollTop? document.documentElement.scrollTop : document.body.scrollTop) + "px");
	left:expression(eval(document.documentElement.scrollLeft? document.documentElement.scrollLeft : document.body.scrollLeft ) + "px");
}	
</style>
<telerik:RadMenu runat="server" ID="RadMenu1" CssClass="RadMenu_Fixed />