Requisites
-A brain
-Basic computer knowledge(such as typing, clicking)
-~1st grade reading level
 
Step 1: Download the Necessary Programs/Files
Jdk 7 - http://www.oracle.com/technetwork/java/javase/downloads/jdk7-downloads-1880260.html
Check "Accept Licence Agreement" and download the proper one. (You might already have this)
 
Eclipse - http://www.eclipse.org/downloads/packages/eclipse-ide-java-ee-developers/keplersr2
Download the version of eclipse for your OS.
 
Minecraft Coder Pack 9.03 - http://download1888.mediafire.com/5ce9sfbpbayg/q97ptg3ng85tpra/mcp903.zip
Download MCP 9.03 (Minecraft 1.7.2)
 
 
Step 2: Extract them to a central place (such as the desktop)
This is pretty simple. Use a program such as winrar or 7zip and move the files into folders (DO NOT LEAVE THEM IN THE ZIPS, THEY WILL NOT WORK)
 
Step 3: Run decompile
For windows, run decompile.bat. In applicable OS's, run decompile.sh in the MCP folder and wait(will probably take a few minutes). It should be decompiled now.
 
Step 4: Run eclipse
Just run eclipse.exe (or whatever it is on your OS) and set up your workspace by selecting <MCP directory>\eclipse
Example: C:\Users\Me\Desktop\Modding\MCP\eclipse