Even as David also describeth the blessedness of the man, unto whom God imputeth righteousness without works, -Romans 4:6
Also even before the flood people where calling upon the name of the Lord.
Nd to Seth, to him also there was born a son; and he called his name Enos: then began men to call upon the name of the LORD.-Genesis 4:6
This question, I think, has a fundamental misunderstanding of the nature of God. God the Father, Son, and Spirit have always been around since before time began. Those who lived on earth before Jesus became the Incarnate God-man could still know God, because He has always been involved in human life. They would not necessarily have believed in Jesus as Savior, in the way we mean today. However, they would have still been looking forward to God's Messiah and been reconciled to God through their faith in God. So yes, they could be saved and have a relationship with God, but they wouldn't have the relationship with God the way that we do now, with the general outpouring of the Spirit on this side of the Cross. For more information, see John 8:56-58, Romans 4, and Hebrews 11.
The Jewish people and the Judaism the religion were the only true faith. Israel was suppose to the beacon of the world and be the nation of prophets and mass converters. Instead however they failed to do this three times. First they were sent to Egypt, second to Babylon, and third the Destruction of Jerusalem and the Diaspora. The Jews suffered harsh persecution in Communist Soviet Union and of course during the horrible tragedy of the Holocaust. After these 2 thousands years of being the lost the Jews came home. Before Jesus existed and you wanted to have eternal life, you were a law abiding, sacrificial Jew, or a God fearing Gentile. Before the Christ man lived under law, no we live under mercy.