Currently - there is no tax treaty between Taiwan and US...
Any payment by US companies to Taiwanese residents are subject for mandatory 30%withholding.
You would need to file US tax return as non-resident, calculate your actual tax liability, and might be able to get a refund.
Please let me know if any clarification is needed.
Unfortunately - no - US consideres China and Taiwan as separate countries.
(a) the term "the People's Republic of China", when used in a geographical sense, means all the
territory of the People's Republic of China, including its territorial sea, in which the laws relating to
Chinese tax are in force, and all the area beyond its territorial sea, including the sea-bed and subsoil thereof, over which the People's Republic of China has jurisdiction in accordance with international law and in which the laws relating to Chinese tax are in force;
source - http://www.irs.gov/pub/irs-trty/china.pdf