Ok let me start for saying that with Digital SLR today and the strides they have made with ISO there is no reason to have noise.
With that said if you do have noise with an image this is something that can help depending on the damage of the photo and the noise within your channels.
First Start by opening your image and going into the Red Channel and applying a surface blur to your Red Channel with a radius of 10 and a Threshold of 12
see image below.
Your going to attack noise on a channel basis so next is going to be your Green Channel with a Radius of 8 and a Threshold of 9
Now it is time for you last Channel the Blue Channel and it has a Radius 5 and a Threshold of 10 as seen below.
This Process adds a very Blurred/Plastic look which is very non pleasing look to me but to try and fix that issue the next step is to try and bring out some of the details with and Un-Sharpen Mask as seen below.
Here is the Before and After below.
Before
After
If this technique does not work for your image I highly recommend the plug-ins listed below.
They have really came a long way with noise reduction technology.