Often times, skin cracks or breaks between the toes are caused by a fungal infection known as athlete's foot. It can cause itching and burning as well.
This type of skin infection should be treated with topical antifungal medication. There are several good over the counter products like Lamisil and Lotrimin. Liquids or gels should be used between the toes, not creams or ointments which create too much moisture.
If you have any doubts, if the infection is not resolving, or if there is any redness or swelling, you should see your local podiatrist for evaluation and treatment. Prescription medication may be needed.