I've been making my computers quieter, both for multimedia purposes (in the living room) and for my own sanity.
Over the years computers have been getting noisier due to increased power usage and this increased heat and number of fans. There are modifications one can make to quiet these noisy computers.
Systems can be made quiet (almost but not quite silent) without major modifications or custom work. For example, my living room PC (which functions as a PVR, DVD player, stereo jukebox, and web TV browser) is an almost silent Pentium III based system using many of the components listed below.