Hubi's Loopback MIDI Driver is a public domain MIDI Driver that allows the output of one MIDI program to act as the input of another MIDI program. You can use it to synchronize QuickScore Elite with another MIDI program running at the same time on your PC, such as a digital audio recording program or another sequencer. It was developed by Hubert Winkler (email address: firstname.lastname@example.org). Instructions are provided in the download file. If you need more information, ask Hubi!
For newer PCs you may want to look at MIDI Yoke, which provides the same functionality as Hubi's Loopback MIDI Driver. Get it here.