Great news! Thanks to Synthex, not only one of the first to build MegaDrum but to make a contribution to the project, MegaDrum is now fully plug-n-play with a PIC18F2550 based true USB MIDI Board. Synthex developed the board schematic and, most importantly, a USB MIDI complaint firmware for it. You can see how it happened in these threads:
http://www.megadrum.info/forums/viewtopic.php?f=3&t=31 and http://www.megadrum.info/forums/viewtopic.php?f=3&t=38
In true spirit of MegaDrum project you don't need to build a special programmer for it but a simple cable with 3 resistors and 2 connectors. Details on how to program the chip using this cable will follow soon.
The schematic and the firmware are respectively on Schematics and Downloads pages.