In Greek mythology, Cerberus was the guardian of the gates of Hades (hell). Its job was to prevent the dead from returning to the world of the living (possible purpose of Cerberus/Smokey in LOST).


As for how Radzinski and Inman heard of The Pearl, I suspect that Radzinski was either one of the original Dharma Researchers or he managed to find a way of communicating with other stations (not so far-fetched, considering that he was able to hotwire the blast doors and knew the locations of many other stations).
Once Radzinksi knew then he would have passed on his knowledge to Inman just as Inman did to Desmond.

It would be important to note that Radzinski may have spent a lot longer on the Island than Inman ever did (and thus had a lot longer to explore the Island), because we know that Inman was actively involved in prisoner interrogation during the first Gulf War, so he would't have joined the Dharma Initiative until after the war had ended.
Whereas Radzinski may have been on the Island since the Dharma Initiative first commenced research there.