Neeraj,
What do you mean by "anonymous users with saved preferences"?
The anonymous desktop does not contain any editable functionality. Remember, the anonymous desktop is shared by all users that are not logged in. Therefore, it does not make sense to allow anonymous users to modify the display profile. Notice that there are no edit/minimize/maximize/remove buttons on any of the channels on the anonymous desktop. This is because the anonymous user has a specific DP that removes these buttons.
Add a portlet to the desktop just like any other channel. This can be done directly to the anonymous user's DP. Add the channel and remove the edit/minimize/maximize/remove buttons.
Users can modify the portlet preferences once they log in to their own account. At this point the preferences will be stored with their own DP.
HTH,
Jim