JOEL - You do not have to be a member of the church if you want an LDS Bishop to perform your marriage ceremony in an LDS Church.
Actually the Bishop can perform the ceremony anywhere you want; but it is preferable to have the ceremony in an LDS Church building or at the couple's home. This would be considered a civil marriage, the same you might have for any other legally authorized minister or public official.
Missionaries are not authorized to perform marriages, but the President of a mission can.