You can upload mp3 and wav files in the forums by just dragging them into the editor or clicking the upload button, or you can paste a link to audio files hosted elsewhere and a player will appear automatically.
For example, pasting in this URL:
http://www.podtrac.com/pts/redirect.mp3/cdn.twit.tv/audio/twit/twit0626/twit0626.mp3
Automatically hides the URL and shows this player instead: