Cognitive and cultural embeddedness: combining institutional economics and economic sociology
According to this, pederasty is sexual relations between two males, especially when one of them is a minor. Other definitions, like the one that JSBangs found, differ slightly. But otherwise, I think you answered the question yourself: pedophile refers to the attraction, while pederasty refers to the act itself.
Please note in the US, sex with anyone under 18 in illegal-- so pederasty lies on a thin line legally. Pedophilia, on the otherhand, is sex with a pre-pubescent child of either gender. Pederasty, as a general rule, has stayed as a structure among gays because it has many distinct benefits. For the younger man, it is an opportunity to learn from someone with more experience-- with sex and the world; it is also a way of helping the younger man as he is in a state of self-discovery.