|MadSci Network: Astronomy|
I'm sorry for the delay in answering your question. I'll start with your last question, because it's the easiest to answer as we know a lot more about the Earth than we do about the rest of the solar system.
By volume, the earth contains 1408.7 cubic km of water -- and 99% of that is contained in the oceans and ice caps (the oceans alone contain 97%). The remaining water is liquid (in lakes and rivers) and gaseous (in the atmosphere).
As for the rest of the solar system, there is evidence for frozen/liquid/gaseous water on other planets and moons, but it's difficult to quantify exactly how much. We think there might be water ice at the poles of the Moon, and the amount of water on Mars (which is there in the atmosphere and frozen at the poles) is a very hot topic for research. NASA is sending probes to the Moon and to Mars to find out more about this.
Further out in the solar system, we know that Jupiter's icy moon Europa is a prime location to look for more water in liquid form: pictures beamed back from the Galileo spacecraft hint that it may contain a vast subsurface ocean underneath an icy crust. Callisto and Ganymede are other icy moons of Jupiter that scientists are interested in investigating. Jupiter and Saturn themselves may have icy and/or rocky cores, and Saturn's rings are thought to be made up of icy particles.
Comets are another source of water in the solar system, as they are mostly 'dirty snowballs': made up of 70% or more of water ice.
I found some of the numbers quoted above at this site ...you might want to look there for more information.
Try the links in the MadSci Library for more information on Astronomy.