You should install Codec Pack All in one.
Codec Pack All in one description:
Codec Pack All in 1 is a collection of codecs that will help you play almost any DivX movie. All you need to see DivX movies: DivX, XviD, AC3...

This codec pack includes:

· Decoder pro DivX 6.1.1
· Decoder pro XviD Koepi's 1.1
· Decoder pro DivX, XviD - FFDShow 17.02.2005 alpha
· Decoder pro MPEG2 2.0.0.0
· Decoder pro titulky g400 2.83
· Decoder pro titulky DVobSub (Win9x, Win2k a WinXP) 2.23, 2.36
· Decoder pro OGG Vorbis 0.9.9.5
· Decoder pro AC3 1.01a RC5
· Morgan Multimedia Stream Switcher 0.99

You can download it from here.