You certainly plan to broadcast some kind of audio material, don't you? Whatever your needs might be, there are basically two typical setups that can help you get going.
NOTE: Always keep your aerial away from your transmitter (especially if it doesn't have its own enclosure), power supply and audio system. If you cannot meet these requirements, you could experience feedback and other RF problems. Interestingly, RF energy can make CD players and other digital devices go bezerk. Try placing 30W-driven antenna next to yours...

If you have a strong enough PC consider using it for managing audio part of your radio station. There are many specialized computer programs available for this purpose. I myself prefer Winamp, which is not specialized for this purpose, but does a pretty good job (the pic is below) since it can play most sound formats, including the most interesting one, MP3:

Winamp supports various plug-ins. Plug-in is an add-on to a program that you can use to add functionality. My favorite is Audio-stocker. It seems to be perfectly suited for broadcasting. It provides FM station like compression, at no additional cost (provided you own a PC and sound card).

A PC with sound card and suitable software CAN actually take care of most of your audio, at least in the beginning. As your station grows you eventually need to purchase stereo encoder and limiter (PC does not take care of this in a professional manner, probably partly thanks to software).

Many professional DJ's that I know hate using computerized audio systems. They say that PC's can let them down (we all know the good old blue screens that Winblows produces every couple of hours or so). There are also other things, most not entirely (if at all) justified.

Beginner would probably start by plugging his CD or cassette deck directly into his transmitters audio input. However this is not a professional way of doing things. Classical setup would be something like this:

-Preemphasis

This is typically part of the stereo encoder itself, it raises level of higher frequencies in audio. Higher frequencies are then attenuated in receiver. This technique lowers level of noise in received signal.

-Low pass filters

Audio signal has to pass low pass filter before it goes into stereo encoder. Audio signal should not appear close to 19KHz as this is where stereo PILOT is and it would cause the Stereo LED on the receiver to flicker as well as receiver shifting to MONO mode. Even if you transmit in MONO, such low pass filter should be used. Why? To limit space that your signal uses on the band. Your signal could become wider than the standard deviation for FM broadcasting, resulting in interference to other radio stations. Interference means you can get busted!

-Audio limiter, makes sure your signal never gets too far from center frequency.

-Compressor, increases your average loudness

-Stereo encoder

Finally, for gods sake, play same great music. Go above the commercial crap everyone plays these days.

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