So where were we? Ah yes, genocide against the Amalekites. I see what you did there. What you are doing is changing the argument to suit your conclusion or not understanding what you are arguing against. I'll give you the benefit of the doubt and say it's probably the latter. Do correct me if I'm wrong.
When first we began it was posited (ooooh, big word in small package!) that christianity teaches peace to people who want to be taught peace and violence if they want violence... I corrected you and then you moved on to the strawman and I figured it would just take less time to do this as a blog as opposed to twidenting back and forth all week. :-)

So first, let's go back to the original issue.

christianity teaches peace to people who want to be taught peace and violence if they want violence.

Again. No. To understand why this is so simple to put down (in my head at least) we need definitions. Actually, just one: Christianity. Christianity is not the Bible. It is a doctrine, a set of teachings, beliefs if you prefer put forth by a man. A man I like to call the Son of God, but you may disagree with me on this point; that man is Jesus Christ. Christianity's doctrine then, is whatever Jesus says. He references the commandments, belief in Him as the Son of God and the only way to God, and repentance of sins. There's also a liberal sprinkling of other stuff we should do. Nowhere (to my knowledge, but correct me if I'm wrong) does He say genocide is ok. Ever. If you disagree with me that this is what Christianity is, then we are forever doomed to argue this point and I might as well move on.

Now let's go back to the strawman.

... but genocide on the Amalekites is peachy? Folks take what they want from the bible. Luckly our morals aren't Biblically inspired.

As presented, it goes something like this: Jesus' teachings make up christianity. Jesus' teachings are in the Bible. The Bible advocates genocide, ergo christianity advocates genocide (if you want it to).
Ahem: No. :-)
Let's ignore the fact that we don't even need to dig as far down as Samuel to see evidence of God's Holy Wrath™ (Noah and the Ark anyone?). Yes, God has instructed Israel (not us) to wipe out a nation or two. Man, woman, child and all. And I do mean all, even the animals. Now that's harsh. However (and here's where we'll certainly disagree) it's not genocide when God does it. It's judgement, and not just plain ol' judgement either. Oh no! It's righteous judgement. Now there are many arguments which could be made as to why a perfect, all-loving God would allow, encourage or do this but I've been typing two hours already. Here's the short version: He's God, he knows better than you. Irregardless, God has deliberately chosen to not deal with us like this for millenia since. And the
status quo definitely flipped the script once Jesus was born (oh yah, i went there).

Which brings me to thing no. the third (I'm not even going to touch the Constantine thing except to say : Wong!).

the OT does seem to be only selectively irrelevant...

The Old Testament isn't selectively irrelevant, you're just (with all due respect) missing the point. it's actually quite relevant, even today. Actually especially today. It teaches us a bit about human nature with the Children of Israel playing the role of us. (Wow, getting long. Still with me?) You see the Children of Israel were God's chosen people but they were stubborn. They'd disobey every so often, be punished, asked for forgiveness, be forgiven, GO BACK AND DO THE EXACT SAME THING, and start the whole cycle over again. We today do the same thing only we call it repentance. Welcome to saving grace of Christianity. Actually, that is saving grace. I tried to be punny just now. It'd take a much longer post to really get into this (and thus this explanation will utterly fail to satisfy you, but hopefully perk you're interest enough to check it out with your local pastor or so). Take home message, we're imperfect, we sin. God loves us and forgives us. He also punishes us because he loves us (kinda sounds like a parent, eh?) because sometimes we just won't get it otherwise.

To wrap it all up (and you should reaaaaally check out the stuff below with other christians/pastors/theologans/the bible :-))
When Jesus came to earth he preached forgiveness of sins, loving your enemy and much cheek turnage (actually just read all of Matthew 5, it's short). An apparent contradiction from the Old Testament where it was eye for eye and

So in conclusion: Christianity does not teach different things to different people. It teaches one thing in many ways, love for God first and foremost, and love for your fellow man next (with those two taken care of love naturally ebbs and flows to the remaining variable in that equation).
Some of us get miss the mark and are either too zealous for God (note the absence of the word love in that description) or love people more than they do God. The latter might not sound so bad but states of mind are equally desctructive (jealousy, lust, addiction vs. religious fanaticism, scorn, condemnatory). The bad thing about this is that they still say they are christians and really some are trying to be. Thing is we as people suck. We're selfish, insecure (and generally all around sinful) and find it hard to kick these habits (because of our sinful nature). That's why you'll find people in church after seeing them in the bar doing, well - y'know. But you know what church isn't for holy people anyway, it's for sinners like you 'n' me. And anyone who isn't a sinner is just there to help, not laugh at you or make you feel bad. If they do, they fail at christianity and you should find yourself another church. And if it's too hard to find one yourself. Pray. I'm sure He'll answer :-)

P.S. Our morals are biblically inspired. :-pppppppppppppppp