If you're looking for an efficient workout that does not use free weights. head on over to http://trainforstrength.com/workout1.shtml is one of the best bodyweight oriented exercise routines there is. Also, try breakdancing...sounds crazy; however, you develop a lot of balance and a good physique to march with (and by good physique to march with, I mean reel in them guard girlies ;))

creatine can help because it adds water weight but i wouldnt advise it because there are a lot of health problems that can occur if you dont be careful. it can chrystalize in your kidneys, water pockets can form in your muscles and a lot more than that has been linked to creatine use. if you dont use a protine powder, start with that if you want to get more muscle.

for goals, a good measure is to squat more than your body weight (1.5x or so your weight)
curl half your weight
and bench at least your weight or more

bench press will do something for you and pullups work a lot of your muscles

dont overtrain, do either a different muscle group every day or do a whole body workout and take the next day off. you will not gain any muscle if your body doesnt have time to rest and regenerate (thats when the muscle is actually "growing")

dont be afraid to eat a lot of food but make sure your diet is clean and healthy mcdonalds will add weight but not the kind you will want. muscle will add weight and raise your metabolism so you will be able to shed a couple pounds that you might gain and you can do some cardio to work it off if it bothers you that much.

be safe, use good form, and have some fun with your exercise
hth

Overall, creatine is very safe. It does cause your muscles to hold water, so the primary concern is staying hydrated. I drink about 30 oz of water during my workout, then mix creatine powder into 16 oz of water, and try to keep myself hydrated consistently between workouts. The creatine makes a huge difference in how quickly I improve my performance.

Glutamine is also helpful, as it can help your body increase production of HGH as much as 6x. I take a creatine powder that also includes glutamine.