One of the most cool things about learning to engrave is that it
takes only a few hours to learn the basic techniques, but you can
spend a lifetime learning and perfecting it. Also, there are few
artistic crafts where so much can be accomplished with so few tools.
You can spend a fortune outfitting an engraving studio, but you can
get started with less that $100 US if you are industrious. You can
also use found materials to practice on, I started with bottle caps
and car parts.
I would highly recommend the sites John posted, as well as a couple
of books.
The Art of Engraving, by James B. Meek
Engraving on Precious Metals by A. Brittain and P. Morton
http://www.amazon.com/exec/obidos/ASIN/0719800226/ganoksincom-20
The Jewelry Engravers Manual by R. Allen Hardy and John J. Bowman.
If you have to prioritize, I would get them in the order I posted
them. The last two are older books, so the tools and language are a
bit dated, but engraving hasn’t changed all that much in a hundred
years. I still refer to them quite often. The first book is a
treatise on the art of engraving much more than the techniques.
Happy cutting!
Dave