Guitar controllers have been around for quite some time. Roland and Yamaha have had guitar controllers and MIDI pickup kits since the 80's.
I should warn you though, depending on your playing results could be less then acceptable in some cases.
You have to play the guitar in a "cleaner" manner. Any kind of accidental strumming of strings results in random MIDI note data for lack of a better description. Nedless to say, the result comiing from your MIDI synth through the speakers could be quite annoying.
I remember watching a show on BBC while living in Europe. They were interviewed Midge Ure (member of Ultravox) where he said he plain hated guitar MIDI controllers because it required him to completely change is playing tecnique.