Yeah, just accepting Jesus existed won't be enough. You need to accept that God is the true God, and from there follow his (Jesus') teachings. If you just believe, you won't achieve salvation. You have to accept him completely and change. As said before, I think that the laws of the Pentateuch, the commandments under which Abraham made the covenant, are the ones by which we are no longer bound. The rest of the Old Testament is a recounting of the history of Israel, prophecies, advice and praise. Its not pick and choose, but those specific laws are no longer in effect because the old covenant has been lifted.
This is what's most interesting of all, however. And what I think may provide you with an answer to Bela's argument that Christian morality is arbitrary. If God has his own moral code that shuns slavery, surely that's the definitive morality? (Of course, it'd be nice if he set that down for us in writing, but perhaps that's the Ten Commandments. I dunno, I ain't no scholar.) Thanks, both of you, for providing such interesting food for thought.
Hmmmmm.... I'll have to think about this... I may ask other christians about this as well, but at the moment I won't answer this. I'll try later on though, when I think I know I can give you a satisfactory answer.