You damned well better keep it seperate. A biology teacher that teaches creationism is teaching one particular religions mythology, not science. For doing that, the teacher should not be allowed to teach science, period.
Perhaps a Christian needs to teach you to spell. "Separate".
There is nothing wrong with sharing one's personal beliefs in the classroom. Teachers of all subjects talk about social issues all the time, and the issue of faith is just an extension of that. You won't ever see me saying they should teach creationism in PLACE of whatever subject is being taught (except in parochial schools, where the curriculum wraps around the bible and prayer) because kids are in particular classrooms to learn about particular subjects.
But IF children are being taught about the "theory" that we have evolved from a "common ancestor" that we share with other primates...a theory that has no basis in fact and is a complete guess based on the fact that we are all similar and share basic gene structure, then I see no thing wrong with touching on the theory, believed by a HUGE number of people in the world, that we were created by a creator. There should be no requirement that children believe this, any more than there's a requirement that they believe we're the grandchildren of Lucy; but they should know the theory exists, and not be taught the lie that it's myth, that it doesn't bear consideration, or that the people who believe it it are stuipd. It's about increasing knowledge, instead of limiting it, and it makes me ill people, claim that teaching children all the possilities somehow makes them more ignorant than withholding information. You don't enlighten children by refusing to give them information, or by passing on your personal opinion about things...in place of truth.