You have a lot of reading to do. The good news is that you have found this website during high school. I wish so much that I would have had the knowledge about training I do now when I was in high school. I am sure the amount of knowledge available here would have helped me be a much better swimmer/hockey/lacrosse player.
Here is a great article on strength training for swimming:
http://www.elitefts.com/documents/power_pools.htm
Basically, there is a long ingrained dogma in swimming about avoiding real strength training in favor of “dryland” training consisting of lots of crunches, medicine ball throws, etc.
Finding and following a good STRENGTH training program will go a long ways to making you a better all around athlete and swimmer.
While this is all well and good, I understand that it may be very difficult to implement a strength program on top of swimming. I would bet that you will only take a week or two off after high school swimming, and then be right back in the pool everyday with your year round team. Just try to get in the weight room a a few days a week and follow a well designed, balanced program. In order to support your swimming and lifting, you will really need to increase your calorie intake, and focus on post workout nutrition.
As a small anecdote: On my high school team, there were basically two types of swimmers. There were the guys that were on year round teams that were relatively small and not all that strong, but kicked ass in the pool. Then there were guys that participated in other sports like football, looked awesome, were very strong, and were also very fast in the water. I would say of the top four guys on the team, three were the small year rounders, and one was a very strong athlete. What I am getting at is there is more than one way to skin a cat. Work hard on your technique and swimming specific skills, but also work hard on being a well rounded, strong and powerful athlete.
I would say to start read everything by Chad Waterbury and Alwyn Cosgrove regarding training, and Dr. John Berardi regarding nutrition. Dr. B’s manual “Precision Nutrition” would probably be very beneficial to you. Eric Cressey has a book called “The Ultimate off-season training manual” that I have not read (going to buy it soon) that sounds like it could help you.
While this was a very long winded post, I hope it will help you in your goals. Swimming training really interests me, and a lot of it has to do with wondering why in the hell some coaches train their athletes the way they do!
Good luck and keep us all updated
Jeff