The difference between Wicca and Witchcraft - a hotbed of debate. As usual, I have an opinion!
Wicca was created by Gerald Gardner in the 1950's. It is based on pre-Christian pagan beliefs, some Eastern philosophy, and Masonic and ceremonial magic. He called this Wicca and started the Gardnerian Tradition.
Wicca is not the same thing as Witchrcraft. I will agree with most witches in saying that the two terms should not be inter-changed, as they commonly are. Its rather like calling a Roman Catholic a Protestant or a Baptist - they believe in the same thing, they just go about it in a completely different way.
As to the similarities and the differences..
Most Wiccans follow the Wiccan Rede as one of their basic tenants. The shortened version of that is "An it harm none, do as you will," which is pretty self explanatory. Along the same lines, they also follow the Law of Power or Three-Fold Law. This is rather along the lines of karma - whatever force you send out will be returned to you three times as strong. Witches, on the other hand, do not follow any such redes or creeds, unless they are a specific part of the Tradition they follow. From what I understand, most find the Three Fold Law illogical (a point with which I, personally, agree).
The other main difference between Wicca and Witchcraft, is the practice of magic. Wiccans generally cast a circle before doing any magical rites or rituals. This merely consists of creating a sphere of energy that surrounds yourself and anything that will be used in the rite or spell. Whereas some Traditions of Witchcraft may use circle casting occasionally, to most Witches all space is sacred and circles are not needed for rites.
Wiccans tend to place heavy emphasis on rhyming chants and ceremony (or ritual), such as having corresponding colors and herbs for a certain spell – or casting a spell on a Tuesday when the moon is full. Witches, however, more often use whatever they have when they feel the time is right.
Those are a few of the differences, and hopefully have helped to straighten out the interchangeable Witchcraft/Wicca. I myself was guilty of calling them the same thing when I first started learning about Witchcraft, Wicca and Paganism - then I learned that there were real and true differences. The best advice I can give anyone wanting to learn about Wicca or Witchcraft? Read, read, read. There are a lot of great books about the subject – however, remember that the writers of Llwellyn books are not the be all, end all of Paganism. If you have to read them, do it with a large grain of salt.