In Douglas Coupland's Microserfs, a discussion about the difference between geeks and nerds came down to 'hireability' - ie, geeks can use their specialist geeky skills to make money, whereas nerds can't. (You wouldn't phone Nerd Squad to come round and fix your computer in an emergency.) 'Nerd' also tends to have connotations of loserdom, unpopularity and social ineptness (think Milton from Office Space), whereas the other main guys from Office Space were more in the geek camp. In 24, Edgar was definitely a nerd, but Chloe's a geek.
According to the definition of both nerd and geek that payndz201 gave us, then I guess I'm more of a geek with some "nerd aptitudes". Geek Nation, live long and prosper!!!