Here are a few good video tutorials on how to decrease noise in Photoshop and PSE. However, the results are much better for photoshop users than PSE users! (Sad PSE user here!) :(
My only problem with this one is on some of my photos the "median" step and the "surface blur" step made my photo look like it was a painting. :(
You have to play around with some of the settings to see what is best for your photo. Also, what I like to use in addition to or sometimes instead of these steps is use the "Reduce Noise" option in the filter tab under "noise" and also the "Despeckle" option in the filter tab under "niose". I like to use "Reduce Noise" because it has an option to "Reduce JPEG Artifact" and a "Reduce Color Noise" option as well. Which was mentioned in the CS2 video above.
Here is an example using ONLY the steps from the PSE9 video
Here is an after shot
Using only "Despeckle" and "Reduce Noise"
This was shot in RAW then converted to JPEG with no additional edits.