A friend of mine had this recipe (modified from this one which he got on the Food Network website)...really tasty:
1 1/2 ounces finely grated fresh ginger
6 ounces sugar
7 1/2 cups water
1/8 teaspoon champagne yeast
2 tablespoons freshly squeezed lemon juice
He experimented with a variety of ginger types, and found that the plain-old stuff from the standard grocery store made the stuff most to our taste.