So, like the title says, how do I install Minecraft Snapshot 12w03a that was released earlier today. I have downloaded the files (Client and Server) onto my computer and I have also unzipped the files. What do I do to install it onto my Minecraft files or to play it? Here's the link to the Minecraft Snapshot 12w03a on Mojang's blog: http://mojang.com/2012/01/19/minecraft-snapshot-12w03a/
First the idiot test: You've bought Minecraft, right? You just need to replace the original .jar with this new one. On Windows it's usually located somewhere in %appdata%/.minecraft which you can get to via the search bar. Keep in mind it's likely to overwrite any mods you may have installed.
In addition: If you have Mac OS X, the original "mineraft.jar" ffile is located in /Users/____/Library/Application Support/minecraft/bin.
Assuming the .jar isn't contained inside the .zip, you should be able to rename the extension and it'll work just fine. Make sure you've got file extensions visible (Google it if you don't) and away you go.