Thanks to Kamikaze and Les for the great info.... now let's take this puppy to USB keyboards. More than a keylogger, I just want to trigger something across a factory floor when a certain string of characters are entered into a database, but the task is the same.

I have done the necessary research and have all the nitty gritty voltage signal requirements for USB communication that has led me to the onboard comparators in many PICs. How do I setup a comparator to take the differential signaling from D-/D+ on the USB data lines and convert that into 0 and 1 in the PIC for further processing? Here is an excerpt that provides most of the details that I need to setup the comparator.
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USB signals are transmitted on a twisted pair data cable with 90Ω ±15% impedance,[9] labeled D+ and D−. These collectively use half-duplex differential signaling to combat the effects of electromagnetic noise on longer lines. Transmitted signal levels are 0.0–0.3 volts for low and 2.8–3.6 volts for high in Full Speed (FS) and Low Speed (LS) modes, and -10–10 mV for low and 360–440 mV for high in High Speed (HS) mode.
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Most of the comparator examples that I have seen only handle one input. I have determined, given the details above, that the reference voltage should probably be about 1.25 volts, so do I use two comparators against the same reference voltage? Or,..... I'm kinda lost on this one, but really want to figure it out.