Irene,
Measurement Studio is simply a plug-in for Visual Studio C++. Calling a DLL is general to C/C++. It usually amounts to #including the .h file that comes with the library, like this:
#include "MyDLL.h"
I found the following website through Google, which is pretty thorough on calling DLLs:
http://www.codeproject.com/dll/XDllPt1.asp
I hope that helps.
Matt P.
NI