there are two ways in which you can achieve the desired functionality. In both ways you will need to do some custom development:
1. You can bind the RadMenu to SiteMap (this is how we do it in our SiteMenu control - you can find the source of this control in : ~/Sitefinity/UserControls/Navigation
Then you would need to handle ItemDataBound event of the RadMenu and you can alter the properties of each menu item as it is bound (e.g. you can read the page name and assign it icon, change the css class and so on)
2. Second way is to built RadMenu from the SiteMap using the typical recursive function for building a tree. Once again, you will have access to all the properties of the RadMenuItem before you add it to the tree collection (Menu) and therefore you will be able to alter its properties, such as icon or css class.
You can find more about RadMenu and RadMenuItem objects here: http://www.telerik.com/help/aspnet-ajax/menu_itemsoverview.html
I hope you'll find this information helpful. Please let us know if there is anything else we can do for you.
the Telerik team
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