I agree with Neko and linda.
A witch is anyone who casts spells. Even Satanists and Christians could be considered witches if they cast spells and do magic, but they aren't Wiccan because they follow a different religion than Wiccans. A Wiccan is someone who follows the religion of Wicca, which is an officially recognized religion just like Christianity, Judaism, Islam, and Buddhism. If you get nothing else from this, remember that "Wicca" is the name of the religion and "Wiccans" are the followers of Wicca. So you wouldn't say, "I have a friend who is Wicca." Instead, you would say that your friend is Wiccan.
According to the Wiccan Rede, which are the rules that Wiccans abide by, Wiccans are not supposed cast harmful spells. The Wiccan Rede says, "And ye harm none, do what ye will." Someone who claims to be a "witch" but who is not "Wiccan" is not following the religion of Wicca. Therefore, they do not have to follow the rede. So they can throw curses at you from across the room. If you think you want to be Wiccan, or you want to know the difference in Wicca and witchcraft, here are some useful pages to read that explain the difference: http://paganwiccan.about.com/od/wiccaandpaganismbasics/a/WWPDiffs.htm
You can simply manipulate and direct energies as you will and enjoy the rest of the magic practices the craft can offer you. If you want to do no harm in order to follow the rules of the christian bible, there is no problem.
There are magic practices you can use ; such as divination, higher magics, spell casting ,etc. The fact you are christian will not give you any bad result.
For an example. If you use a healing spell, god, or the universe as few of us say it, will not be mad at you and will not punish you, and as the christians believe if you do something good - like healing which is extremely good and helpful, and if done with a good motive you will even be rewarded. Yes, christians believe that god sees and remembers everything, and good people who do good things will get their goodness back by getting some kind of a reward, it is kind of like karma.
Simply learn and see what magic can offer you, and enjoy it because there is no problem with doing it as a christian. ;)