this is a really really crude way of going about but what you can do is take a 1/8'' cable, and run it from your headphone jack to your line in jack. Set garageband to record from your line in and hit record. Start playing your video. After it is recorded, cut out the part you want and bounce that to itunes.
I actually found a neat little program called TuneBite that allowed me to record the video into another application, then extract the audio, and save it as an mp3.
Yes I Know That There Is One Way That You Get A Audio Transfering Software That You Can Extract Any Percent You Like. It Is Very Easy To Control I Know One Software Whose Name Is Xilisoft Ipod Rip .