The code for this project can be downloaded here
The code is written in PHP, and uses a MySQL database. A cron job is set up to post each day’s horoscope to the Tumblr account.
This is completely free software, so you’re welcome to do whatever you like with it.
Contributions and feedback are appreciated.
Update:
A git repository for this project is online now at https://github.com/PeerInfinity/Weighted-Horoscopes
Eliezer Yudkowsky can make Chuck Norris shave his beard off by using text-only communication
(stolen from here)