Finally got working the network part with the emulator above on Win7.
Simply download latest OpenVPN package, unpack end extract x64 tap driver. Then go to Device Manager->Action->Add Legacy Hardware, then point to the .inf file of the driver extracted. Et voila! Now I can connect from host to emulated OS as in doc above.
Note: if the driver from previous install approaches is present in Device Manager (typically as "unknown device"), it needs to be removed manually, "update driver" does not work.

The .bat file included to .zip package needs to be adapted for a new driver path and also "run as Administrator".

Also works fine with latest QEMU binaries for Win that could be found here: Qemu On Windows