Rar. Beware. I've now got the M&S USB missile launcher working under Linux. I hate libusb, it's very badly documented and seems to assume you know the USB spec inside out. Anyway, usblauncher-0.0.1.tar.gz does the appropriate magic (if crudely) and includes a basic GTK2 Perl program to control it.
Ian Jeffrey has also produced some code that works in much the same way, but it's only a command line example and I couldn't see a license that allowed redistribution attached to it. It looks like he went about things in much the same way as I did though.