This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
The most important piece of the puzzle is the static method Integer.parseInt(), which takes a String as an argument and returns an int; you can then add these ints.
As far as doing something with every other one: sure, just call nextToken() twice per loop, and throw the result away one of the times. You have to be careful if there are an odd number of tokens, of course!