If that direct link does not work then you can go to http://www.mp3raid.com and search for Mainstreet Electrical Parade. It ought to be the second or third down in the list. You'll have to enter the "Proof of being human" style prompt and then you can get to the mp3. There is a button below where it shows the playing file that says "Download". Right click and "save target as" to your desired location.
There are countless ways to do this, most of which will require at least one type of conversion application. For example, you can download the youtube video in its native .flv format, and then using an application like QuickTime, export the downloaded video as an .mp3 audio file. Or, you can use an audio capture application that will "listen" to any audio output coming from your computer (including any audible sounds caused by other applications) and save that as an audio file, often .wav or .mp3. Much like a screen capture tool, this works similarly to hitting "record" with a blank audio cassette in an old FM stereo system.
There are seemingly countless applications out there, for purchase and for free, that promise to be able to convert multiple file types to other multiple file types.
I'm currently working on my own application that will convert the sound of Gilbert Gottfried's voice into that of Morgan Freeman, so that audiences everywhere can once again enjoy Aladdin. :lookaroun