Last updated on 21-Jul-2010 01:28:21 PM
It sounds like you are half way to solving the problem yourself. You have already noticed that the ball always goes off the table. Now you need to angle your bat to counter the sidespin and direct the ball back onto the table.
Have a look at James' question on combating side spin serves and see if you can follow the advice I gave in that answer about how to practice returning this type of serve.