Help with DJ programs and audio programs

I am beginning to getting into DJ'ing for parties and weddings and am looking for any help I can. Obviously I have Itunes that all my music is in. I am wanting to know if there are any programs that may integrate with that or what equipment I would need so that while my song is playing through my amplifier/equalizer and over the speakers I can be listening to other songs, either in my itunes, just downloaded on limewire, or like from other cd's when I'm looking for the right song so that I can add it next so it will be the next song in the playlist (kind of like when you have the dj type cd playback machines where one is playing and you can put another one in to find your song. Do I need a special piece of equipment to do this? ALso if I do what is a good economical one for a beginning wedding/party dj and how would I go about hooking it up so that I could add that cd or whatever to my music playlist for the next song? Also I wouldn't mind having one that I could do a little beat mixing on the fly with.

 

I used limewire as an example as I DO Not use Limewire. All my songs have been paid for one way or another I can assure you. I was using it as an example. Guess a better example would have been a song from another cd waiting to queue.