Very simple achievement to do now. I did it today using this channel:http://www.dailymotion.com/video/xeoj30_gh-van-halen-dance-t...
The search feature on the page is very crap. For a few of the videos it told me it couldn't find anything, so unfortunately you will manually have through search through each page on the profile until you find the one you want.
Every single song in GH:Van Halen is there with an expert FC.
Simply sync up your mic to your computer speakers. The way I did it was play the video until it got to the first word - hit pause just before the first word, waited for the game to catch up and hit play on the video. May take a few attempts for each song.
I also found that when it came to the freeforms - she was fantastic at them but the mic didn't pick them up very well, so quickly yank the volume on the speakers up a bit and it will award you a tonne of points.
Credit goes to siavash from x360a for finding the channel and of course freqrexy for her awesome voice :)