How to go about making a keyboard with arduino as the controller
You mentioned you are simply looking for the easiest method. The awesome thing about Arduino is its Open Source nature; so naturally anything you think of, someone probably has already constructed. Anyway, if you just Google: "keyboard library for Arduino", the first hit looks as though this is a library that essentially trivializes the difficulty in your project:

http://arduino.cc/en/Reference/MouseKeyboard

However, I'm unsure of the HW set up in this (i.e. does this connect solely through USB? Or perhaps you require a shield?). I'll leave that research up to you.

There is also the question of how you will detect all those key presses on a keyboard. You mention "making a keyboard", so I assume this HW will be constructed by you. You'll have roughly 60 (I'm guessing) buttons to keep track of. In this case, you should use a Key Matrix. Here's an article for research on this:

http://pcbheaven.com/wikipages/How_Key_Matrices_Works/