huw- Well, first I would caution you about creating accounts for other people. We sort of...frown...on that sort of thing. It's a security issue since you would know everything that went into the creation of the account, and only the person using the account should know those things.
Beyond that, you need to have a business account to be able to add a Federal Tax ID. If you don't (and our system can't match the number to the business name), it won't take the number.
