How to add minecraft mods manually

The Brown family has had just tons and tons of odd difficulties in doing something that supposedly everyone is doing: Adding mods into the minecraft client. So here is a step by guide of the method I found that works for me. For this walkthrough, I will specifically detail how I got the "TooManyItems" mod to work.
(Found at http://www.games-utilities.com/toomanyitems-mod-for-minecraft-1-4-5/)

Note also, that I have just written a java utility to make the process more point-and-click: --)) modder (((---

Please note first of all, that these instructions are originally written for MacOS/UNIX/similar machines. If you have an ms-windows machine,you can probably use most of it, but you may have to translate it a little.

Note also, that this is a guide for how to do things by typing at a command prompt. So, on the down side, there's less pointy-clicky. On the plus side, you should actually be able to copy-and-paste instructions here!!

Step 1: Go to the minecraft directory

First of all, open up a Terminal window, and go to the main minecraft software directory.
On macos, that should be:

cd "/Users/$USER/Library/Application Support/minecraft/bin"OB

Step 2: make a copy of the working jar file

If you've never added any mods, I suggest
cp minecraft.jar minecraft.jar.orig
However, if you have already added some mods, you will probably want to change it to someting like "minecraft.jar.modded"

Step 3: extract the existing one

There's no need to install other funky programs. If you have a proper install of java, you should also have the "jar" utility installed. So, you can do the following:
mkdir moddir cd moddir jar xf ../minecraft.jar

Step 4: extract your modfile

You probably put the mod in your downloads directory. So, to go with the example, you can now do:
jar xf ~/Downloads/TooManyItems*

Step 5: combine for the final result

For some mods, the first "rm -r" is supposedly optional, but probably you should just do it every time. Here's how you put together the two things:
rm -r META_INF jar cf ../minecraft.jar *
And that's it! You should now be able to start up minecraft with your added mod. If it doesnt work... don't panic, just copy back the file you saved, in step 1. You DID follow all the steps, right?

It's also beneficial to keep around the original, "pure" minecraft file, as mentioned, because some mods allegedly conflict with others. So in that case, you can extract from the original file, rather than a heavily modded one, and make a special new minecraft.jar for some non-cooperative mod.

At some point, I may write a java program to make this process more pointy-clicky. I'm actually halfway done with it. Feel free to send me an email if you dont see it after april 2013!