This site includes a Classical Guitar Dictionary: English-Spanish and English-Italian:
http://seicorde.org/

Here's a sample: English - Espaņol

gauge - calibre (m)
grain - veta (f)
grained (of wood) - veteado
groove - ranura (f)
guitarist - guitarrista
guitar-maker / luthier - guitarrero
gut - cuerda (f) de tripa (f)
gut string - tripa (f) - cuerda de tripa

This is just one of thousands of sites listed in the 2000 Guitars Database:
http://www.guitarsite.com/database/

Add your site: http://www.guitarsite.com/addsite.htm