my guess is to wait and see if it starts to sprout roots while sitting in the water (which should probably be changed daily). you may want to leave the glass and stem near a sunny window. maybe a bit of growth hormore would help things along. once the roots are pretty good looking (there should be more than one, maybe a few should have "branches" or off shoots) then stick it in a pot in the same area that it was sitting in the water. keeping it in the same place should minimize the shock of changing from the water enviroment to the soil enviroment. once it is a little more established in the soil you should be able to move it to it's more permanent home. good luck and let us know how it worked out!

Mostly good advice from Andrew, except waiting. If you wait too long the cells that can generate new roots can atrophy or become infected with bacteria.

I strongly recommend getting some rooting powder from a local garden/hardware store, then do a corrective cutting on the stem to give it a nice clean fresh surface at the correct 45 degree angle, apply the rooting powder, then put it in an appropriate damped growth medium like peat or vermiculite until it generates some roots. You also use shredded newspaper or wadded up paper towel as a growth medium.