You can refer to the website much information to share:
Minecraft - Minecraft Mod – Minecraft Global
From height 0 (platform) to 127 (the cloud)
Your location, health, inventory, experience, Game mode (creative / survival), time and weather
Seeds of the world
All the monsters and animals
All items lying on the ground
World Mod Downloader 1.6.2 can not save
Spawner cage. They all spawn pigs. This is a server error / limit.
The records in the jukebox.
Spawn location if it is moved (by the administrator or by sleeping in a bed).
Players other people of course
install
Open your minecraft.jar * with an archive tool like 7zip or WinRAR.
Put the class files you just downloaded in there. Overwrite if necessary.
Delete the META-INF folder if it exists in the jar file.
Close the archive and save if required.
Make and play!
Download Mod for Minecraft 1.6.1
Download Mod for Minecraft 1.5.2
(if you work with Java 7 installed)