What contains the most energy at 100 degrees celsius.. water or steam?

The steam. It would have to go through a phase change and give up a bunch of energy to turn back into water at 100. Assuming you mean equal mass of water and steam.

Same question for ice. How much energy does it take to melt 1 Kg of ice at 0 to water at 0?
you need to specify volume or mass
water, there would be more water than steam
water has more mass, more mass is more energy
does water not turn to steam at 100 degrees
For the same mass, steam would contain more energy as it also contains the latent heat of evaporation, which the water does not have.
the steam because the distance between particles of steam is further than of the water. thus, the particles of steam can move very randomly, freely, and fast due to the large spaces between particles. because of their very freely motion, they contain more energy than water which can only move by gliding to one another. this automatically shows that steam contains more energy than water although at similar temperature (100 degree celcius).
Obviously steam contains more energy than the water. because steam contains latent heat energy extra than the hot water at 100 deg celsius. Latent heat energy means is the energy required to convert hot water into steam at same temp(100 deg C). It is the energy which is equal to product of mass of water and latent heat of steam.

Latent heat = Mass of water x Latent heat of steam (540 erg/gram)
Water changes to steam by the time it hits 100 degrees Celcius. To get water higher than 100, that may be a pressure cooker that does not allow steam to escape. If you can keep water in the liquid state to 100 degrees or more, it has explosive energy.
water at 100 degrees would contain more energy as the transition to steam uses energy and steam is by definition a lower energy state (otherwise fluids would not turn to gasses.and some don't)

Steam at that temp if memory serves is 540cal/(g)(degree C)

The energy required to change liquid water to steam is only 1cal/(g)(degree C)
at 100 degrees C water IS steam.. Duh!
The same mass of water as steam contains considerably more energy at 100 C (41.1Kj per mole more) due to the latent heat of vaporisation which is the energy needed to turn water at 100 C into steam.
There is a huge amount of really bad science in many of the answers above - I blame the Thatcher years of Tory education cuts! Also the question is incorrect, since steam is water, but at a different energy level - I assume you mean water as a liquid as compared to water as a gas.

Putting energy into a system raises its activity - i.e. the more energy the more active the system. Of course, the energy has to come from somewhere else outside of the particular system, since it cannot be created or destroyed.

To alter water from its liquid state to its gaseous state requires a phase change, which requires a huge input of additional energy known as the latent heat of vapourisation. The actual temperature at which this occurs is dependent on the pressure in the system. This energy is given up in the reverse process, as witnessed by the huge amount of burn damage caused by steam as compared to hot water at a similar temperature.

Therefore, it is absolutely clear that for the same mass the steam must contain much more total energy. It is this additional energy which causes the molecules to move faster and therefore transform into a gas.
Steam ofcourse, you wouldn''t get water at 100 degrees! It would evaporate into steam!