Low-light no flash photography?

[lale]

I'm hauling my camera along to my sister's class theatre performance tonight, and neither flash nor a tripod can be used. I know it sounds pretty hopeless, but any tips (apart from pumping up the ISO)?

[sybren]

Fast lenses and/or image stabilization. And bring something like a bean bag or a cushion, so that you can use a chair in front of you as a sturdy base to shoot from.

[oldwolf]

lowest f/stop possible and highest iso you're comfortable with.

[lale]

Thank you so much for your help! I used your tips and got some really fabulous photos of all the kids-- I won't post them because I don't know how their parents would feel about that, but I know there were a few of my own sister I was very happy with!