You can use the following:
1. Web horoscope services, I don't know any but you can look at here.
2. RSS/Atom - subscribe to the RSS channel(s) and parse by your needs
When you create user's account just put additional info like date of birth in DB/users.properties or any other place and after a user is logged in, take this info and query. Show retrieved data using some "widgets" (Flex, JSF, JavaFX, DoJo, RAP ...).