When you changed the speed, did you click on the Maintain audio pitch button? May still not be suitable but might help.

As for the audio, generally, an avi or other imported file has the audio and video linked, but you can unlink these which is under the Clip / Unlink Audio & Video, or, if you hold the ALT key down when you select the video file, it will move it separately from the audio. To check if they're linked, when you click on the video timeline, the audio should highlight too, if not, you need to either relink the clip, or shift click on the audio as well.