Using ipo for jumping isn’t recomended. You can configure the ipo from the ipo editor to not take into account any axis except for vertical, just delete the curves for the offending axis. But this will only let you get to a certain height, and doesn’t work well for dynamic objects. Another option would be to parent it to the empty as pooba said, and make the empty dynamic. But this wont let you jump to higher platforms because the empty is still on the floor.
Most people accomplish jumping with force, but this doesn’t scale well on different computers. I.E. some people will be able to jump high enough to beat the level, but those who are blessed with fast enough computers will not. And those with slower computers will have rediculously good jumping ability! But anyway, to do it this way:
*add a collision sensor to your cube
*for MA: put in the material name that the floor has (if it doesnt have a material, add one
*connect that to an and controller
*add a keyboard sensor, set it to the jump key
*connect this sensor to the same “and” controller the collision sensor is attached to
*connect the “and” controller to a motion actuator
*give the motion actuator an appropriate force along the vertical axis. You usually have to make it fairly big, because this force is only applied on one frame.