The Diamond Martini is a wonderful (and very simple) variation of a Vodka Martini. The difference between the two is that in the Diamond the vodka is pre-chilled by placing it in the freezer. Don't worry, the liquor will not freeze. Also, be sure to use a frozen cocktail glass, taking it out of the freezer just before pouring the drink.
One other tip for this martini (and any martini for that matter) is to use the best spirits you can get. These cocktails rely solely on the liquor and without any fruits or other ingredients, there is no masking the taste of a low quality spirit.