P. Murphy,
Reinforcement of the floor joist will need to be determined on site. Most homes will handle the weight. You will want at least 2" of wood both under and above the cut in the floor joist. Make sure the tub gets the proper venting. Venting makes all the difference in how things drain.
Terry

: Just moved into a new house which has a 1/2 bath on the 2nd floor which is just above a full bath on the main floor. We're want to install a tub int the the 2nd floor bath. Pretty sure that after I tear up the flooring, I'll have to run the tub plumbing through the joist. Will joist require reinforcement and what other tips would you have for plumbing this new tub into the existing 2nd floor drain system?