Sleep in a bed and it becomes your spawnpoint.
Although, Single Player Commands has a bug where typing "home" will not take you too your bed, but to your original spawnpoint.
Chat with our AI personalities
You can set TNT off in Minecraft Beta by clicking it, or by triggering it with redstone.
No, Minecraft Realms are 100% vanilla as they are provided by Mojang.
/setwarp (name of warp)
you cannot set up permissions in a normal minecraft server. you must have a bukkit server to use permissions. check the bukkit forum for more info.
In order to play Minecraft with friends, you need to set up a server. You can either set one up on your own computer, or you can rent one from a company for fairly cheap prices.