This question is impossibly broad. You have to nail down some details first: How many simultaneous users will there be? What kinds of distances are involved? Are the videoconference sessions one-to-one, one-to-many, or many-to-many? How good does the quality need to be — small YouTube-style windows on PCs or full-size classroom screens? Who’s going to support it?Last but not least, how much money do have to spend on it?