Did you choose a science project? Is your due date still April 20?
I think you were onto something with your original question. The strawberries would have the same amount of DNA because that is constant, but the amount
of DNA that you purify from a berry might be different depending on whether you used unripe, ripe or over-ripe berries.
Isolating DNA is a challenging process. I'm sure you have heard of scientists who try to isolate DNA from 3000 year-old mummies or 20,000 year-old frozen mastodons. Sometimes it works and sometimes not.
You could use the very simple DNA purification method that uses kitchen chemicals, http://www.sciencebuddies.org/science-f ... p015.shtml
I don't know if the ripeness of the fruit affects the amount of DNA that you can purify, but I think it would be an interesting question and it is something that could be done in one day. The only problem I see is in determining how much DNA you have isolated from each fruit. You could try weighing it if you have a sensitive scale that can weigh in milligrams. Otherwise you could just take a close-up picture of each DNA sample and compare them by eye.
Let me know what you are doing and I will try to help more.