Originally Posted by
Michael
I'm pretty sure that both spellings are transliterations of the same pronunciation in Mandarin. "Peking" was the transliteration using the old Wade-Giles system, while "Beijing" is the transliteration using the newer Pinyin system that was introduced by the PRC government in the 1950s or so. Both should be pronounced the same way -- which is admittedly counterintuitive for those who don't know how the systems work.
This Wade-Giles - Pinyin conversion table indicates that Pinyin "Beijing" would be written as "Peiching" in Wade-Giles.
The Wikipedia entry for Beijing claims that the romanization "Peking" came from French missionaries 400 years ago, predating both standardized romanizations and a sound shift in Mandarin that changed k to j.
Chinese restaurants in the US serving the well known roast duck dish still usually call it "Peking duck" rather than "Beijing duck".