Below is a link to a fairly good article:

http://www.egullet.org/tdg.cgi?pg=ARTICLE-campgrappa

The article explains the basic process and includes differentiation for reds and whites.  My personal opinion is that unless you have access to a true "Grappa Master", you will need to piece your answer together - especially here in the U.S. where home distillation of alcohol for consumption is illegal.  Grappa is one of many regional applications of fruit and vegetable based distillations.  Italians make Grappa, Swedish make Aquavit, the French make Calvados (distilled hard cider)and others make Vodka, Whiskey, etc..

What they all have in common is that a distillation process is utilized in making the beverage.  I would direct your attention to another really informative web site http://homedistiller.org/.  That should get you familiar with all aspects of distillation.  I remember this site from some years back and it has really been built it out nicely.

Given you have the means and the knowledge; I believe the difficulty in distillation is in producing a refined, smooth, and drinkable product. Once again, http://homedistiller.org/ offers some good tips.

Now, with all that said - here in the US, home distillation of alcohol for personal use is ILLEGAL.  Dealers are allowed to sell distillation units for the purpose of water purification and essence extraction, but there are strict legalities around that activity.  The section of homedistiller.org on legality has a real nice explanation on the law here in the US.

The information in this article is for informational purposes only.  Any guidance provided herein should in no way be taken to mean that we at M&M Produce and Juicegrape.com condone or promote the activity of home distillation for producing alcohol for consumption, as we recognize it is illegal to do so.

- Nick Coppola
juicegrape.com