Run a single GUI virtual user. You cannot call a WinRunner script from a LoadRunner script. You can call WinRunner to WinRunner or take advantage of the fact that all loadrunner scripts are C functions to call one from within another, but the cross of the two do not meet.
Referring to the OSI model, LoadRunner APIs, sockets excluded, are generall layer 6 (presentation layer), while a GUI API is layer 7 (Application layer). Generally speaking you would initiate the call from higher on the OSI model to lower. Even if you could call a WinRunner Script from wtihin loadrunner, this would be a call from a presentation layer api (layer 6) to an application layer api (layer 7); it would be bad form.