| The little green adapter is for devices that can already talk both USB and PS/2 - as you note, it just allows physical connection.
One small warning - a USB port is supposed to be limited to 500mA of current (2.5W). Not all USB ports enforce this limit, but some get snotty if you go over it. Others just ignore the problem. (Actually, this isn't entirely true - USB guarentees 100mA of current, and up to 500mA after negotiation with the USB controller).
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