From what I gathered, it's the same as WoW currency. 100cp=1sp 100sp=1gp 100gp=1pp. Of course, I only got into silvers so it could be different above that.
As an aside, they also have gems and karma. Gems are used for the in-game store (i.e. real moneys) and karma is a reward from dynamic events that you use to purchase specific event reward items.