Hi Jimmy, I hope I can answer your question without getting too long. The short answer is that "film grain" is a function of the film composition itself. The slower films like 100 ASA usually have less film grain than ASA 400 film. It is caused by the chemical that makes up the photo sensitive layer of the film.
Normally "noise" is associated with digital pictures. There is more than one reason for noise to be in a digital picture, but it is similar to the film issue of speed of the camera at the time the picture was created. Although some digital cameras have more noise than others due to the image sensor being used.
Noise and grain are very similar when you compare the pictures of each. The technique to remove film grain will work on noise also in some cases. There are filters and techniques for use in Photoshop to remove both grain and noise. I use a commercial application called "Neat Image" that does a good job of reducing noise and grain. It is available here http://www.neatimage.com/
. I highly recommend this program if you have a need for this process.
There are several different sets of actions for Photoshop that offer noise reduction. One is Digital Deluxe but I can't find the url of the site where I obtained it. I'm sure others will reply and give you more helpful information.
I hope this has helped you.