well, if you want it to move up and down without slowing down at the ends of its travel you could use this code.
do
if object position y()=>5 then _dir=0
if object position y()<=0 then _dir=1
if _dir=0 then ymove=-0.2
if _dir=1 then ymove=0.2
position object 1,object position x(),object position y()+ymove,object position z()
sync
loop
In this code, it will move an object (object 1) up and down by 5 units continuously, with the 'ymove' variable setting the movement speed, and the '_dir' variable so set the direction so that it reverses at the end of each movement.
I will do a smoother movement peice of code when I get home (at school now) back l8rz