Follow these steps to get the LSDj to work on your computer.
Get full stable version of LSdj by donating, or using the demo.
Have it saved to your computer desktop or folder of gameboy games.
Download a PC Gameboy emulator
List of Gameboy emulators for the PC http://www.zophar.net/gb.html
Gambatte – after messing with a LOT of different emulators, this one is super accurate on all channels. the save file management can be a pain, but it's worth it. Plus it works on PC and Mac http://sourceforge.net/projects/gambatte/
BGB – pretty good emu which LSDj works on for sure.
open the BGB emulator if that is what you have, drag and drop the lsdj.gb file onto the emu screen or navigate to the load area of the emu. make music with LSDJ.
Default BGB controls for LSDj on keyboard are
s – a button (hold a to shift notes and such) arrows for control shift is select button enter key is start (to play song)
thats all you need I think.