Conditionally Hiding Menu Items

I am using asp.net with C#. The site is on the intranet and hence the first user authentication is done at the domain level for site visitor.

One verifixed, I want to show / hide menu items based on that user's role. The user ID and their roles are defined in my back-end SQL Server DB.

All users see the following:

<asp:Menu ID="NavigationMenu" runat="server" CssClass="menu" EnableViewState="false"
                    Orientation="vertical"
                    width="100%" StaticMenuItemStyle-HorizontalPadding="9"  StaticMenuItemStyle-VerticalPadding="9"><Items><asp:MenuItem NavigateUrl="Default.aspx" Text="Home"/><asp:MenuItem NavigateUrl="About.aspx" Text="About"/></Items></asp:Menu>

Power users see the following:

<asp:Menu ID="NavigationMenu" runat="server" CssClass="menu" EnableViewState="false" 
                    Orientation="vertical"  
                    width="100%" StaticMenuItemStyle-HorizontalPadding="9"  StaticMenuItemStyle-VerticalPadding="9"><Items><asp:MenuItem NavigateUrl="Default.aspx" Text="Home"/><asp:MenuItem NavigateUrl="report.aspx" Text="Reports"/><asp:MenuItem NavigateUrl="Extract.aspx" Text="Extract"/><asp:MenuItem NavigateUrl="About.aspx" Text="About"/></Items></asp:Menu>

How can I accomplish this using site.master? Any help would be greatly appreciated.

Thanks in advance.