'File' >> 'Export movie' >> 'Audio as MP3' or 'Audio as wave'
Then you can import the audio portion into a new project. This does assume (you say you are using Movie Edit Pro) that your video/audio file has been brought into the editing program first.
Step by step:
import the complete clip
export the audio as above
close and exit
start MEP again
import the new audio only file
This isn't any way MEP can act directly or remotely on a file on the hard drive. Note also that MEP is a 'non-destructive' editor -- after your audio export the original file remains unchanged.
ADDED: Perhaps easier, as you want to end up with only the audio, is to import the full clip and then delete the video track. You will have to first un-group audio and video using the little broken link chain icon above the timeline.