Lucifer and Satan are technically seperate entities who have become blended due to cross-religious confusion.
Here's the dealio:
Satan is an angel, a very important angel at that (one of the Seraphs, I think). He lives with God and is quite loyal to his maker--hard line loyal, in fact, believing that god and his angels are perfect and that humanity does not deserve to exist as it does.
So, throughout the Bible, Satan seeks to try and prove that humanity is no good, that they have no true loyalty to God, etc etc, and that way, God will purge them all in another great flood and then there will be cake for everyone. Except for us. Because we're dead.
So, Satan is the "advesary" of mankind, but he is not the devil. That's the interesting things--Jews don't believe in Hell, right? There's not exactly a specific afterlife for the Jews, so that means there is not a Hell either. So, Satan's role is a bit more interesting, because he's technically on God's side--he's like the other voice in God's ear, telling him that we are all scum and need to be purged.
Lucifer, on teh other hand, has almost NO Biblical base. He's not portrayed as the devil or anything in any specific biblical texts, and is, in fact, a purely Christian figure, concocted by the Church at some point during the Dark Ages and built larger and larger ever sense. He's based quite a bit on many Pagan gods and images, in order to demonize and villainize them.
Since Christians have an actual "Hell" that is seperate from both Earth and Heaven, Lucifer is said to be king of Hell, and his name is, in Christian termonology, synonomous with Satan, as their roles are ultimately the same--try and lead humanity down a path of sin and temptation and away from God. It's just the small details that really differ.
So, the important parts to take home are: Satan is an angel, and is an actual Biblical character. Lucifer is a fallen angel, is a heavily Christian-based entity, and is the caretaker of hell. I.E. the devil.
Satan is NOT the Devil.