Kung Fu or Gong Fu?

Both actually refers to the same thing. The Chinese government introduced the new pinyin system in 1958, which replaced the old Wade-Giles system used since mid-19th century.  As a result, materials published before 1979 are mostly in the old system, and material after 1979, including the current materials, are in new pinyin system.  Here are some of the more common terms used in Daoist Kung Fu in both system:

Old New  Chinese Meaning
 Tao  Dao  道 Path/ Way / Law
 Taoism  Daoism  道家 Dao school
 Kung Fu  Gong Fu  功夫 Degree of skill
 T'ai Chi  Tai Ji  太极 Grand supreme /Totality of Yin and Yang
 Ch'i Kung  Qi Gong  气功 Energy practise
 Wu Tang  Wu Dang  武当 Name of the mountain


reference: http://en.wikipedia.org/wiki/Wade%E2%80%93Giles

old-new conversion table: http://library.ust.hk/guides/opac/conversion-tables.html