Spawn point

In 1.5 snapshots (and I am pretty sure 1.4 as well) you can use either the command block or enter the command /setspawn to reset the spawn. That is the easiest way for vanilla (I think you can also do /setspawn <x> <y> <z>). As for bukkit, you need a plugin like essentials which does the same thing, not sure about the coordinates though.

For multiplayer you can make your server a bukkit server (google it!) and then install a plugin which can change your spawn such as Essentials core

http://www.youtube.com/watch?v=6o5sQ8VMv5g

Is that helpful?

If not, try Googling "How To Set a Spawn Point in Minecraft"