|MadSci Network: Earth Sciences|
I didn't know the answer to this one, but fortunately NASA has a good description with information about their Earth Observing System. This includes a PDF on Sea ice with lots of information about polar ice. According to them: "Together, Greenland and Antarctica contain about 75% of the world's fresh water, enough to raise sea level by over 75 meters [250 feet], if all the ice were returned to the oceans." Of course that's not enough to cover all the land on Earth, although it would cover about 1/3 of the total land area. There are a bunch of other complications in setting an exact number, but this gives you a good idea of the size of the effect melting all this ice and snow would have.
Try the links in the MadSci Library for more information on Earth Sciences.