yeah use swimplan.com.
As part of your profile you can input the times from time trials it asks for on the site in the fitness test section so that the generated workouts are more suited to your fitness level. You can also select what kind of gear you have available, pool length, time frame you want to do it in, and what kind of strokes you know how to do. When the site generates a workout it will take those variables into account. You can have up to 5 workout plans generated per day and save your favorite ones.
As you get better you can tell it to generate more difficult ones or easier ones if you are feeling tired or fatigued.
It is a really good site. The workouts are similar to what I was given in college.
The workouts also have instructions for each set on how to do them (can turn it off if want). They are also highlighted according to target heart rate ranges as well.
Don't start off too hard though. Swimming can be very demanding on the body. I remember reading an article once about how people who weren't prepared for triathlon competitions most often died during the swimming phase from heart attacks.http://www.usatoday.com/news/health/2009-03-29-triathlon-heart_N.htm
A good way to check on yourself is to monitor your heart rate during the exercise and keep it within the target zones. That way you can see if you are pushing yourself too hard or not.