Minecraft Mods and You
Minecraft mods work well in both Alpha and Beta, but depend upon using the right version to work. (Check References below for a link to a list of mods you can try out and what versions of the game they work with!) Just like a key to a door, both can be perfect specimens, but they will only work properly when correctly grouped together. If you have a mod that works for Alpha, it will not work with Beta and even more disturbing is the mod will more than likely damage whatever World you load, perhaps even permanently corrupting the save entirely.
How to Install Minecraft Mods
For this guide I will be installing the Optimine mod. Before we begin, in order to use the mods you download, you must make sure to install them to Minecraft correctly. This part can be tricky and requires the Minecraft client and a program that can access .zip files (such as WinZip or WinRAR). If you play the free Minecraft Classic version or simply prefer to play through the browser online, you cannot use any Minecraft mods. You must download and run the client after having bought the game to be able to access and utilize mods in Minecraft. (If you do not own a copy, check out this guide on Bright Hub to see how to get one today!)
Follow the Creator’s Instructions
Before installing whichever mod you like, be sure to read all the information the creator of the mod provides to ensure you know how to install the Minecraft mod properly. In my case with Optimine, it said to both copy the mod files and delete the META-INF folder within the minecraft.jar archive. In order to do that with Windows, you need to be able to see hidden files, as well as see and edit hidden file extensions. Once you have done that, you are able to locate the required files you need to tinker with.
If you have Windows this step is the easiest part. Simply open up the Search or Find option on your computer, (commonly found in the Start Menu), and Search for: "%APPDATA%/.minecraft/bin". It should pop up with a window that looks similar to the image on the right. Make a back-up copy of "minecraft.jar" in a safe place, just in case something doesn't work out quite right.
Back within the .minecraft/bin folder, rename the "minecraft.jar" file to "minecraft.zip" which will allow you to access it with Winzip, WinRAR, etc. (Windows 7 users may be able to access .zip files without any extra programs.)
Open up the .zip file you just renamed and locate the "META-INF" folder. Delete it. (Remember, if something goes wrong you can always replace the whole file with the back-up you made previously) Open up the mod you downloaded, in my case the Optimine archive pictured on the left. Select the files from the download and extract them to a folder, or even the Desktop. After you decompile the archive into the location of your choosing, select the files and drag them into minecraft.zip. A pop-up will probably ask you what you want to do with the duplicate files, select the "Add and replace files" option.
Now rename minecraft.zip back to minecraft.jar, close all those windows you may still have open, and load up the game. Go to Single Player and press "Create New World" (as to avoid damaging any previous worlds before you can see if everything worked out successfully) and take a look around. In my case I noticed instantly that the processor lag was extremely diminished, so I knew right away that the Minecraft mod was installed correctly!
Now you know how to install Minecraft mods! Some may require additional steps, but the principal remains the same. Locate a mod you like, follow the Creator's directions, and always, always make a back-up copy of your minecraft.jar before you tinker around with anything. If something ever goes wrong just replace the botched file with the safe copy and it will go back to normal.
Scaevolus, "[V1.3] Optimine (FPS Boost) [OPTIMIZATION] *UPDATED*", https://www.minecraftforum.net/viewtopic.php?f=25&t=132717
"Mods – Mincraft Wiki", https://www.minecraftwiki.net/wiki/Mods
Screenshots provided by ramen4life