The main treatment methods for depression:
Biological - IE prozac, and other drugs, I have mixed feelings about them. I would recommend persuring other
Behavioral - Changing your routines, making time to get out and exercise, making time to get out and hang out with friends. As a person who has been through a depression, I can tell you that this is very effective. It took me meeting a very special girl to snap out of my depression and get me back into shape.
Cognative - Not incredible effective with most people, it's basically a therapist telling you that you are thinking illogically and tries to change the way you think about yourself, and ultimately tries to get you thinking away from depression. Usually works better for phobias.
Social - Group therapy, not as effective for depression as it is for trama, axiety, eating disorders, and other "society" influenced illnesses
Psychodynamic - Fruedian method. Basically sitting for hours on a couch talking with a therapist who is trying to drudge up some deep down repressed emotions and memories. Very expensive, seldomly effective.
The cheapest, and often times most effective means of helping someone with depression is simply snapping them out of their routine that they are in. If they are sleeping all of the time, then drag them out of bed and make them get out and do something. Exercise is very helpful in helping depression as well. Get out and run, or hit the gym.
Also, many family insurance plans provide a certain amount of hours allotted for "mental health". If you friend is under an insurance plan of his own, or is still under his families insurance, have them check into it. I should cost nothing if they have this service.