Minecraft launcher? It should prompt you to update automatically. BukkitUpdater plugin? Here. CraftBukkit AutoInstaller? Here. If you want a sure-fire way to have your plugins update automatically... Then you're out of luck. Most plugins require you to manually update them.
That's contradictory. Minecraft.jar is what you play on - it's the client. craftbukkit.jar is your server - it's what hosts the server for others to connect to. Which one are you talking about?
I know this. I'm talking about the fact that the launcher itself downloaded the client files and updating them on the server updated and the user.
Пень! New launcher download a client file of Minecraft, I want itself MY LAUNCHER downloading MY CLIENT on my server.
You want to make other players who join your server use the same exact client as you - mods, texture packs, etc? That's not currently possible, to my knowledge, though add-ons to Spout allow you to do similar things. You'll have to experiment with it, yourself, to find the right combination of plugins to begin to accomplish what you want, if I'm understanding you correctly.