I don't understand what you're trying to do.
Your method returns a DataSet. Your type is a LinkDataSource. Logic would lead me to believe that you cannot set a LinkDataSource = to a DataSet...they are different Objects.
All the information you need on the LinkDataSource and any other .NET controls can be found in the
MSDN Library. This resource should get you pointed in the right direction....there are multiple articles on the
LinkDataSource there. I recommend bookmarking the MSDN Library and using it as your primary resource when developing in .NET.
-Frinny