Baseboard on two different floor levels.
Well, the easy solution would be to cut the trim shorter in the room with higher flooring, but I am guessing you are asking because the trim on the tile is already present. What is the junction like between the two rooms? Are you going through a doorway? or does the flooring just change from tile to wood? If there is something like the casing of the doorway to breakup the transition from one floor to the other, I would just put down the trim like normal, nobody would notice the difference from one side to the other. If you aren't that lucky you have a couple of options:
1: You might be able to get away with lineing up the top of the trim and covering up the gap at the bottom with some quarter round.
2: You may also be able to glue a piece of filler material to the bottom of the trim (assuming it is going to be painted). Just make sure the front face of the trim and filler are flush, if you did a good job, the seem will be invisible after the paint.
3: Install some decorative molding on the wall, this serves two purposes, first it provides a good method of defining where 1 area ends and the other begins, and second, it breaks up the transition so that you don't see the height difference.
4: Custom trim ($$$)
5: Redo the trim in the tile area (Atleast the part that is continuous with the transition)
6: Taper the tile trim down to the new trim. This will only work if the taper is very long.
7: All else fails and it just has to be "done"... hide it behind furniture (yuck... can hear my father in the background: "if a jobs worth doing...")
Thats the best I can come up with off the top of my head.