Multimedia System

Does anyone know how I can go about creating a multimedia system for my computer? If I don't construct two smaller bookshelfs to accompany a subwoofer, is there a way I can combine the use of a subwoofer with my existing speakers? My main concern is how to power the speakers, and how I could use appropriate connectors. My existing speakers use a small, narrow plug, such as those that come on inexpensive headphones. Any advice on how I could integrate/build a subwoofer and two small speakers into a multimedia system would be greatly appreciated.