Hi friends. Since the old "Garritan Studio", virtual midi drivers have been discussed and used over this forum.
Today is mostly un-necesary the use of them since Finale, Sibelius and Notion support VSTi. Also any host out there.
But, in the case you were using a Notations editor without vst support, or want for any reason connect Standalone to another program, you will need a virtual midi driver.
The problem is that the mostly used ones, MidiYoke and Maple, are not disegned for windows 7 64 bits.
So, in case you are using this OS, now there is a very nice solution. Loopmidi do the same than the mentioned mididrivers. Additionaly you can create or delete any number of midi ports from the system tray without reset the system. I have tryed it, and appear very nice.
You can download it, in case you need it, here (it also works with 32 bit OS)