If you have an iMac or MacBook, you can use the optical drives in those computers to rip discs to your Mac Mini. There are 2 ways of doing this, provided both computers are on the same network:
1. You can instruct the Mini to use one of your other Mac computers as a remote optical drive. In theory, this is the preferred way of doing it, but for reasons I don't remember, I had trouble with this method.
2. Quit iTunes on the Mini. Open iTunes on your other Mac, holding down the "option" key while it is opening. It will then ask you to choose an iTunes library to open. Navigate to the hard drive on the Mini, and then go to Music -> iTunes -> iTunes Library.itl and choose that file. You are now controlling the Mini's iTunes library on your other Mac, and you can use that Mac to rip your discs directly to the Mini. Just make sure to quit iTunes on your other computer before you try to open it on the Mini. Only 1 computer can access the iTunes library directly at a time.
There are probably other ways to do this, as well.