Best advice I got was this:
ISO 800
Aperture as wide as it'll go
Shoot
Noise isn't too much of an issue in gig shots. It tends to lend atmosphere and, if there's a smoke machine going makes little difference!
Have a look at some shots a friend of mine took (he's on here but not seen him for a while, TommoR). He used this advice with a Sony a300 (so with nowhere near the high ISO performance of the 500D) and the results were great...
I'm sure he won't mind me linking to his shots.... (!)
LINK