Geeks have the intelligence and proficiency of Nerds but branch it out in any feild related to an area of interest. For example; if said Geek enjoys computers they will also enjoy anything related to the computer field including things that, if they were done by a guy that spends 6 hours a day working out, would be "cool". Geeks also make excellent Hackers because of their social abilities. Geeks have the advantage of being very capable socially, but usually only among other Geeks are they truely themselves.
They are often the most intelligent in one field and become quite obsessive in that particular area (see: Trekies). The problem nerds have is that they are the most socially inept of the three classes.
That Nerd really likes playing with his Star Wars action figures.