VISA is a kernel mode driver, so just copying the files over and registering them will not work. You need to use the installer to correctly install VISA, since this involves not only copying the dlls, but also dependent components, config files and also manipulating the registry. the visa dlls are not COM based, so registering them won't work.
Use the VISA
runtime installer that is available for download.
Hope this helps
Bilal Durrani
NI