My divorcewill be final Feb.2008. We have been separated since end of Sept. My question is do we have to file jointly or can we file married but filing separately? We each have a child living with us. He claims one, I claim the other.

You never have to file jointly, even if you are living together.

For 2007, your status is married. You can file only as Married Filing Jointly or Married Filing Separately. Since you are getting divorced, it is safer to file as MFS.
Yes, you can claim one child each.