Help with adbrite please?

from it’s terms and conditions:
"For non-U.S. taxpayers, this
information includes without limitation either a signed
certification that the taxpayer does not have U.S.
activities or a fully-completed Form W-8 or other form,
which may require a valid U.S. tax identification number,"

How am I to get a valid U.S tax identification number, if I’m not in the U.S? What does it mean by the first option?

See original post by xrachel.louisex