Hello Pan hal,
In Silverlight 3 there is a DataForm item which is a close match to the fieldset from asp.net, which you can find information on here:
This is mainly used for databinding scenarios, but should probably fit what you're looking for.
As far as a Frame, this depends on what functionality you are looking for. If you want a movable frame/window type object, RadWindow
would suit what you are looking for. For a standalone frame, like a content item which you load other controls, etc., into on a page, you can use a Border and set its child to whatever content you would like to load.
If you need a frame to display regular HTML content, you could utilize the RadHtmlPlaceHolder
to this end, as it allows for displaying HTML content within your Silverlight application.
Let us know if this helps and if there is anything else we can assist you with.
the Telerik team