I just passed 642-871 exam last month, but the exam itself will be closed after two months and replaced by 642-873.
I have not taken the 640-863 exam.
My question is, in order to get CCDP certification, must I pass 640-863 before February. 2008 (when 642-871 cancelled)?
No, your 642-871 will be valid for 3 years. Validity of passed exam is different from exam being replaced or retired.
Check the last Q&A in this link http://www.cisco.com/web/learning/le3/le11/learning_about_certifcation_exams.html