Outdoor or indoor it will not make a difference. Last Saturday (Aug 9), I was talked into going to get some pics for my niece at an outdoor concert/fair/air balloon event... man, I tell you, I almost had fun (ok certain things aside, it was fun!).
Besides the pick-pocket attempt, and later the teen's hand that I caught trying to get into my backpack (almost broke his hand then and there, he was hauled off by his friends crying like a baby), the constant pushing and shoving and finally the 200 decible screams of wildly excited girls that usually end up being 3 inches from your ears, you can have a good time... maybe.
Right now, I can guarantee you that a P&S is going to get you MAYBE a 1 in 200 chance of a clear picture. From all the pictures that I saw of people beside and around me, thats a fair estimate. These events are just either too far, too dark and too fast for an average P&S to get anything meaningful.
I had the D200 and 70-200 lens, and to be honest, I thought I would have trouble, but I found people unusually respectful of my equipment and the biggest issue I had was to stop getting tired from carrying it around and being pushed just as I took the pic, over and over.
If you want half reasonable pics, nothing short of a dSLR and a long lens is going to cut it. The event that I was at was on the South Shore or Montreal in a town called St-Jean-Sur-Richelieu and the bands there were Creature, Hedley and Tokio Hotel:
Bill, lead singer of Tokio Hotel:
Wear comfortable shoes, be rested before as I felt like I ran a marathon after standing there for 4-5 hours!
Edit: I wondered what a mosh pit was... but it became apparent as soon as I saw it... hilarious.
As for settings... you are going to need a camera that has low noise at higher ISO and a fast lens (F/2.8 or numerically lower). Average settings for the pics I have above are ISO between 800-1250 (I should have gone to ISO 1600!), aperture at F/2.8. There is no "one good" setting. Your dSLR will tell you what you need to get the proper exposure. Flashes during the concert are normally NOT allowed, but since one is normally over 50 feet away from the subjects, they are all but useless anyways (I do not know what they will allow backstage, though!).
Bring plenty of storage (enough for several hundred pictures) and extra batteries if you have them. In one very long day, I went through two 8GB cards and three batteries. Finally... get there EARLY and find a good spot to shoot from.