Make sure you have the latest Winamp
(5.05 at the time of this reply).
Are you using a DSP/Effect plug-in?...
1. Winamp > Ctrl+P
2. Plug-ins > DSP/Effect
3. Select (none)
Maybe the following DirectSound config. Tweaks
Otherwise, a speed playback problem is usually a sign of outdated or corrupted sound drivers. If you have a soundcard go the manufacturer's website for updates. If you have an on board sound chip, go to the website of your computer provider or the manufacturer of the mother board.