How do you control an ASP Menu to show different users different node elements

Hi
I am using an ASP Menu control in a web application, but what I don't know is when a user logs in to the application how do I show different users different options in the ASP Menu control. The menu control is connected to a siteMap. 
For example, if user A is a simple user then he can see Menu Items 1 to 4 in the menu control, however, if a user is user B, then he can see Menu Items 1 to 10 using the same siteMap and ASP Menu control.
Please help, I am scratching my head on this for the last few days.
 
Thanks
 
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