I do this all the time, as I am in the process of creating all-midi versions of a bunch of progressive/fusino tunes from way back when.
I use a freeware program called YTD Video Downloader, which I got from downloads.com, which is run by CNET magazine.
It not only allows conversion between a bunch of different formats, I also use it to download videos from YouTube - which is its main purpose. Then I use its conversion functionality to convert the videos into MP3 songs, which I can then import into Sonar, and also burn to CD to listen while I am driving my car.
There are a ton of such programs out there - I use the YTD Video Downloader because of its additional ability to download the videos from YouTube - INVALUABLE tool for me.
Hope that helps,
Bob Bone