Writing a lot of documentation today, and I'm kind of a grammar dork, so:

A. I.e. means "that is" (to say). E.g. means "for example."
I.e. is an abbreviation for Latin id est, "that is." E.g. is for exempli gratia, "for the sake of example." So you can say, "I like citrus fruits, e.g., oranges and lemons"; or, "I like citrus fruits, i.e. the juicy, edible fruits with leathery, aromatic rinds of any of numerous tropical, usually thorny shrubs or trees of the genus Citrus." In the first sentence you are simply giving an instance of a citrus fruit; in the second you giving an explanation. E.g. simply indicates an example; i.e. specifies, explains. Compare: She loves to read non-fiction, e.g., reference books and how-to books vs. He had one obvious flaw, i.e. his laziness. [Dictionary.com]