Your question about whether it is wrong to read the Harry Potter books is one that many young Christians have faced. In these books the imaginary character Harry Potter attends Hogwart's School of Witchcraft and Wizardry where he learns about possession and casting spells on people. Although this series of books is purely imaginary and the witchcraft in them is not technically the same as real-life witchcraft, filling our minds with things that closely resemble insults to God is not a good idea.
In working with ancient Israel, God consistently condemned witches, witchcraft and all things associated with the occult. In Exodus 22:18, God said, "You shall not permit a sorceress [witch, KJV] to live." In Deuteronomy 18:9-12, He adds, "'When you come into the land which the LORD your God is giving you, you shall not learn to follow the abominations of those nations. There shall not be found among you anyone who makes his son or his daughter pass through the fire, or one who practices witchcraft, or a soothsayer, or one who interprets omens, or a sorcerer, or one who conjures spells, or a medium, or a spiritist, or one who calls up the dead. For all who do these things are an abomination to the LORD.'"
God hates these things because they represent people turning to Satan for their needs instead of to Him. It is a violation of the First Commandment in which God says, "You shall have no other gods before Me" (Deuteronomy 5:7).
In deciding whether to read these books, ask yourself, "Why would a Christian want to learn all about something he or she should never do and something that God hates?" There simply is no good explanation for reading books based upon witchcraft (technically correct or not) if one wants to honor and respect God.
While the answer to this question was prepared by ministers who have studied the Harry Potter books and read portions from them, actually reading bad books or sinning a particular sin is not mandatory before counsel against such practices can be given. When someone learns sufficient information to determine that a particular act is displeasing to God, he or she need not continue doing that thing in order to make sure it really is sin.
If you would like more information about the Harry Potter series, read the article, "The Bible and Harry Potter: Occult Fantasy in Perspective," in the January/February 2002 issue of the Good News magazine.