VLC (initially VideoLAN Client) is a highly portable multimedia player for various audio and video formats (MPEG-1, MPEG-2, MPEG-4, DivX,
mp3, ogg, ...) as well as DVDs, VCDs, and various streaming protocols.
It can also be used as a server to stream in unicast or multicast in IPv4 or IPv6 on a high-bandwidth network.
Here are some key features of "VLC Media Player":
It is a free cross-platform media player
It supports a large number of multimedia formats, without the need for additional codecs
It can also be used as a streaming server, with extended features (
video on demand, on the fly transcoding, ...)
Requirements:
QuickTime 6.5.2 or later
G4 processor/Intel for smooth MPEG-2 decoding.
MP4 Converter
16 MB 
$ 29