As a Lutheran minister myself, I have a bit of knowledge on the issue! ;) "Clergyman" tends to be a general term to refer to a religious leader that operates in a pastoral role. A Catholic or Orthodox priest, a Protestant minister, a Jewish rabbi, and a Muslim Imam can all be categorized as "clergy". These are the people "set aside" to be religious leaders. I agree with Su Ki that it tends to sound more formal and old-fashioned - and bear in mind that in some denominations, you have female clergy, who don't like to be called a clergyMAN! ;) In Christianity, you have a number of denominations, generally divided into Catholic and Protestant. (Orthodox is kind of its own thing, but tends to fall more into the Catholic category.) A "minister", in the American sense, refers to an ordained religious leader in a Protestant denomination - one wouldn't necessarily call a Catholic priest a "minister", but rather a "priest" or "Father". "To minister", as a verb, means either to "attend to the needs of someone" or "to act in the capacity of a religious leader."

It's almost impossible to say. Even within Christianity, every country and every type of church has its own conventions - there are many, many variants of Christianity in many countries, and each one uses words slightly differently. As a general rule, I would advise you to use 'minister' rather than 'clergyman'. Clergyman sounds a little old-fashioned, and is quite restricted in its use. 'Minister' is a much more general type of word.