Yes it is possible. Although as I remember you are on a PC, I can't give you the full inside track/software you will need, i can at least start the bowl rolling.
You will need to download the youtube file(which is a FLV). then you will need to bring it into a editing package so that you can seperate the audio from the video. You may need to re-encode the FLV file into a file that your editor can understand(like a AVI or WMV file).
Sorry I can't help more but I am sure a PC head will come along to help you along. or google, editing youtube videos on a PC.
P2