If you listen to lecture podcasts, you may have learned that listening at 1.5 speed is not only faster, but may actually hold your attention better. It's relatively easy in Windows Media Player. Here are additional directions for Quicktime and iTunes from Wikipedia's wikibooks section
QuickTime Player version 7 and higher (free) for Macintosh and Windows also permits speed control on playback of MP3 and some other types of audio files as well as MP4 (video). To use this feature, go to Windows -> Show A/V Controls and move the slider anywhere from 1/2 to three times normal speed. The ability of QuickTime Player to vary the playback speed of MP3 and MP4 files means that it is possible to play any audio or video podcasts at a slower or faster speed than normal. By right-clicking on an audio or video podcast in iTunes and selecting "Show Song File," the selected file can be opened and played with QuickTime Player instead of with iTunes which does not provide speed control.