Eggnog is essentially eggs, cream, sugar, nutmeg (and perhaps other spices), and some sort of liquor (whiskey I think is the usual culprit), blended.

Here in the grocery stores at this time of year they sell cartons of stuff they call eggnog, which is sweetened, spiced, egged milk. Of course they pasteurize the eggs. It's dreadful stuff.

Here are a couple of recipes online for the real thing:

recipe 1

recipe 2

Alex