Nerds are smart, people who lack much of a social life. They often have very few friends. Nerds don't talk much, and don't expect others to talk much to them. They are usually nice people, but don't have the social skills to go out and meet new friends.
Geeks are different from nerds in the fact that they have social lives. However, these social lives are often spent pursuing some passion that the geek is obsessed with (i.e. Yu-Gi-Oh!). They spend all their time thinking about their one obsession, and play it in all of their free time. Geeks are usually only friends with other geeks, and attempts to converse with geeks is futile, unless, of course, you want to talk about Star Trek or whatever the certain geek is obsessed with.
Examples of geek obsessions are Star Trek, Yu-Gi-Oh!, Magic the Gathering, StarCraft, and basically any other RPG.
Nerds spend most of their free time studying, while geeks make free time so they can play Dungeons and Dragons.
Nerds care what others think of them, but geeks are almost oblivious to the existence of those outside of their geek clan.
Based on all this, I would have to conclude that it is easier to befriend a nerd than a geek, but a geek would probably be a more interesting person.