Indeo was originally developed by Intel, but was taken over by Ligos a few years ago (v4/v5).
http://www.moviecodec.com/codecdownload/indeo.shtml
http://www.moviecodec.com/download/codecs.shtml
The original Indeo 3.2 codec comes included with Windows (98SE/ME/2k/XP), but Intel no longer supports it.
The latest Indeo package for XP is no longer free:
http://www.ligos.com/estore.htm
However, the older/free Ligos Indeo codecs are still usable and I've never had any problems with playback.
What's your video card?
Do you have the latest drivers?
What are your settings in Winamp > Prefs > Video (Advanced section)?