Brand new series on Minecraft Modding with ModLoader.
First of all you need to download to sources called

MCP [Minecraft Coder Pack] : 64BIT [SEARCH FOR LATEST UPDATE]
Eclipse : 32BIT 64BIT [JUST PRESS DOWNLOAD]

Install eclipse. Once finished go to step 1.

1. Create a new folder called anything you want.
2. Put all the files in the latest version of MCP that corresponds your Minecraft version inside the folder.
3. Open the jars folder.
4. Force update your minecraft to the version that corresponds to the MCP version. [MCP 7.23 = MC 1.4.5] etc.
5. Drag both your bin / resources folder to the jars folder that you already opened.
6. Download the latest version of ModLoader that once again corresponds to your Minecraft version.
7. Install the mod ModLoader inside your minecraft.jar folder inside the jars folder. Be sure to delete META-INF!
8. Go back inside that folder and click on decompile.bat. Wait for the process to begin and when finished.
9. Open up your Eclipse.exe shortcut / real file. Navigate to the location of the eclipse folder inside your folder that you created for example. C:/Users/CompName/Desktop/MCP/eclipse/ OR You can browse.
10. Press OK to complete the process. Once opened follow every step.
11. Press Client and open to net.minecraft.src there you should see the main files.
12. Now you are ready to start modding! Please wait for the next blog post of this modding tutorial.

Good Luck!
~ Twinklez