Dealing with noise, especially when shooting at high ISOs, can be a frustrating thing to do. It can be done by playing with exposure, let me direct you to this blog article by Actionwatcher.

If you use PS (most of us do) the easiest thing is to rely on a plugin. For many months I used to have Neat Image, it was OK. Then I heard about Noiseware and I am quite impressed how it deals with knocking out the noise, still preserving detail. I highly recommend it. There's a trial version, so it's safe to try before purchasing.

Disclaimer: I have no stock shares of Noiseware's :)