I'm not sure whether you are asking where the Measurement Studio files are or where the NiHp34401a files are.
If the former, the Measurement Studio files are installed to the Measurement Studio directory when you install the product.
If the latter, the easiest way to add the files to your project is to run the Measurement Studio Add/Remove Components wizard inside Visual C++, expand the IVI Specific Drivers node, and check NiHp34401a.
The driver consists of 2 pieces, the C++ API and the underlying C driver. The C++ API is implemented in a .h file, a .inl file, and a .lib file. The .h and .inl files are in the \MeasurementStudio\Instr dirctory with the .chm that you mentioned. The .lib file is in the \MeasurementStudio\Lib directory.
The underlyi
ng C IVI driver is installed in your \VXIPnp directory. This directory is typically at the root of your C: drive. The C driver consists of a .h file, a .lib, and a .dll. See IVI documentation for more information about the structure of the C driver.
I hope this answers your question. If not, please repost with more specifics.
David Rohacek
National Instruments