Describe exactly how you created it. If you created it in the Address Book
interface, it's no wonder. Create contacts in the Contacts folder. Moreover,
if you create it in a Contacts folder that's not marked as an address book, it
also won't show in the Address Book interface.
Okay, so you created a contact record for someone. Did you also specify an
e-mail address in that contact record? After all, you are trying to send
them e-mail so there must be an e-mail address listed in their contact
record.