Hey guys, I noticed some of the people are saying that the tutorials are a bit out-dated, so I here's a new one (1.4.7)
1. Install MCP, any recent version of Java Development Kit, and Eclipse. I assume since you're reading this that you've seen videos on how to do this or have done this already.
2. After MCP is set up and the source has been decompiled, run Eclipse.exe. A box will come up asking for a workspace. Nextto that, there is the browse button. Click that and browse to the folder "Eclipse" that is in your folder with all of MCP's contents and select it.
3. Eclipse will then open with the workspace you selected. It will be black and you will have a few tools on your screen.
4. Now once you open GuiIngame, you need to add a few things before we add any real hacks.
5. Now that we can check keys, we can actually start.
We're going to want a title for our client. (I'll name mine "Derp")
Title
We will add our GUI above
Code:
if (this.recordPlayingUpFor > 0)
{
this.mc.mcProfiler.startSection("overlayMessage");
var33 = (float)this.recordPlayingUpFor - par1;
blablabla, etc.
...
and below
Code:
GL11.glPopMatrix();
this.mc.mcProfiler.endSection();
}
Creating our Title
Now to make our menu better, we need some booleans.
Since storing a bunch of booleans in this file is a bit messy, we will make a new file to store them. I will name mine "var" since it's short and easy to remember.
Create a new java class file similiar to the one here.
Make sure it's in this package (So it won't throw errors and such)
Since the boolean is static, it can be accessed by other files.

Add a the menu boolean as shown. You don't have to add = false; at the end since by default booleans are false, but I do it anyways. It's a habit :P
Now that you've set up your boolean-holding class, put the drawrect from our main menu inside an if statement like this.
Code:
if(!yourvariablefile.menutoggle)
{
drawRectHere;
}
Adding ! before the boolean means 'not'. So if the menu is Not open, it will draw the rect around the title like we told it to.
6.Now that we have a pretty title, we're going to add a basic menu.
7. The menu and title are done! Now for the basic hacks.
Dem hax
Make booleans in your boolean-holding class for "fullbright" and "fly"

Use this as a reference for any future toggle
Fly
Navigate to EntityPlayerSP
Under the public void "onLivingUpdate" add this:
8. That's pretty much it. This is how basic clients are made. Follow a similiar setup as this and you can do quite a lot in a client.