In Acts 2:14-41, Peter indeed preaches to the Jews. Many Jews are saved that day.
But how can that be? I thought Judaism was a legitimate means to salvation???
Judaism is a legitimate "means" to salvation. It's just too bad the religious leaders of that day weren't teaching it. Jesus did, and they called Him a fanatic, and had Him killed for it. Jesus didn't change how people would be saved... He simply enlightened them all, unlike religious leaders who were power tripping by showing everyone how "holy" they were.
Some today would argue that Judaism still cannot save. In technicality, they are correct, as we are saved by God's Grace, through faith in Jehova. Neither Christians, nor Jews have a legitimate claim that the other party is not going to Heaven.
The religious leaders of that day focused on the Law of Moses. Particularly, they were majoring in the minors. So much so, they lost sight of what the Law was given to accomplish (to set the Jewish people apart from the others in the region, as well as to prescribe Godly living). Jesus brought the focus right back where it needed to be: love the Lord, your God; and love your fellow man.
The religious leaders of that time had never taught the masses to believe in God, demonstrate it with faithful deeds ("good works"), and show love toward your fellow man. These religious leaders were like so many Calvinists today who are consumed with getting into arguments with others over false doctrine instead of actually applying Jesus' simple commands!
So do we Christians need to witness / preach to the Jews of today? Only those who don't believe in God. I'd presume that's not many of them.