Dave Johnson has recently posted an interesting article on taking better photo in low-light condition. He suggests shooting at the lowest possible ISO all the time.
“In ordinary conditions, stick with the camera’s lowest ISO level, since that’ll give you the least digital noise. But when you notice that the camera is recommending a really slow shutter speed (less than about 1/30 second for handheld shots with a point-and-shoot), crank up the ISO. Just remember to drop it back down to the lower value when you’re done, so you don’t accidentally capture a month’s worth of pictures at ISO 800.
Another thing to keep in mind: Most digital cameras don’t allow you to adjust the ISO, or any other setting for that matter, when you’re in Automatic Exposure mode. To tweak the ISO, you’ll want to be in Program, Shutter Priority, Aperture Priority, or a Scene mode.”