Zen is a path to spiritual fulfilment. In order to follow it you need to be able to do two things: sit on your butt and breathe. How hard is that? Do you need to be a buddhist to do Zen? No. Zen and Buddhism are kissing cousins but they aren't married. Any Christian, Jew, Muslim, or atheist can study Zen without comprising his or her beliefs. There are three things that will help along the way: great faith - not faith in a Christian sense but simply a firm belief that the Zen path will lead to enlightenment; great doubt - you must be prepared to take nothing for granted and examine everything for yourself from the ground up; and great perseverance - Zen is not instant enlightenment, it takes years of constant effort. Travel the path and enjoy!