If I were you I would just ask if shes busy over the next day or two. You can be sure she will have a free hour or so... then just come out and ask "Thats good how about we go and grab a (insert coffee/go for a walk/ exchange body fluids etc.) ?" She may ask (though probably wont) something to the effect of "Is this a date?" Say "I don't know, maybe it is maybe it isn't - you'll have to come along and find out!"
Or if you cant muster the courage to try that one ask for her number in or after a class, if she questions you about it just say some crap like 'just in case I need to call you about some of the concert stuff'. Then try the similar routine over the phone a couple of days later. Perhaps open with something like "Hey (insert cute chicks name), I'm bored out of my mind and I'm taking you prisoner... were going to get some coffee!"
Dont worry about the prospect that she may have a boyfriend, if she says she does say something witty along the lines of "Oh ok, is there some kind of waiting list I can sign up to so if things should go sour with current partner I may be considered as an alternative?" That has actually worked for me once, I kid not. Two weeks after I told the girl she broke up and she called me and asked if I was still interested in filling the 'now vacant position'.
