"I am getting an exception when I try to map a class name with different table name in hibernate .hbm.xml mapping file. However I don't get the exception when the class name and table name are same." I think that is the point: the names should be the same...if not, then they are different classes. If you really want this, maybe you could try some sort of interface trickery.
If you think I misunderstood you, please elaborate and post the hibernate config file.
Stu