In terms of rights-grabs, do be careful. In most cases, you can't shoot if you don't sign, but sometimes you can get them to change some of the stipulations. If you ever end up shooting on assignment, but feel the contract you're being made to sign takes away too many rights, its possible to argue that you were forced to sign the thing under duress (no prior warning, short time in which to decide, etc), which nullifies its validity, but is a very tricky case to make. I've only seen it work a few times.
I've been shooting concerts for various publications and sites with my K100D pretty regularly for over a year now, and its never let me down (
http://www.flickr.com/photos/dantekgeek). The best advice I can give you is to learn to love the manual setting (and use the green button or AE-L custom function to have quick access to auto exposure). Using center-weighted metering, you want to look for about a -1 to 1.5 ev indication in the viewfinder, and you should be good to expose the artist and the background fairly well.
Good luck and welcome to the exciting world of shooting shows!