I recently modified my XBox with a Xecuter 2.6CE chip, this is a quick run through of how I did it. All the information you need is out there I am simply trying to collect it together.
Please be aware, if you open your xbox you invalidate the warranty! I am in no way responsible for any damage you cause to your xbox. You will need to be competant at soldering, and a confident computer user to even think about attempting this.
These instructions will only work for an xbox 1.6 and an Xecuter 2.6CE chip, if you attempt this with a different combination you may well cause damage to you xbox.
To find out what version of the xbox you have check out the version detector
For a mod chip visit a supplier such as mrmodchips
If you have any further questions or queries I suggest you start on the forums of xbox scene
The first step in modifying (modding) the xbox is to physically open the box and solder the chip in.
Once the mod chip is installed and the Xbox is back in one piece the next step is to install a bios.
The Xbox has a sort of operating system called the dashboard, the dashboard runs when there is no game in the drive. You will need a new dashboard to run programs from your Xbox.