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Step 1: Materials and Tools
Note: The amount of each component is in the [#]. Most of these parts can be bought at your local Radio Shack or The Source (by Circuit City). As for the fan I suggest you find an old computer and rip one out of there as it would be cheaper than buying one for $10. Overall this project should cost about $10 to $20 depending on weather your able to salvage some of the parts.
-PC cooling fan, must run on 5 volts, any size 
-39 Ohms +/-5% Resistor (Orange, White, Black, Gold) 
-NO/NC (SP/DT) Switch 
-USB Cord 
-Hole Saw (optional)
-Screws and Screw Driver (optional)
The reason for the "(optional)" is because there are many ways you can build this project, chose the way that works best for you.
Step 2: Modding the Cabinet
How you manage to retro fit the fan and holes is totally up to you, I just suggest you keep the cutting neat and tidy. In total three holes will have to be drilled, one to allow air to flow freely into the cabinet; and another to hold the fan which will be blowing air out of the cabinet. Also Depending if you cabinet has a hole for cords (from your system Ex: power cable and audio/video cable) you will have to drill or cut that out as well.
Once the holes are drilled all you need to do is insert the fan and screw/glue it in place; be sure the air flow arrow (located on one side of the fan) is pointing out of the cabinet. The NO/NC (SP/DT) switch will need to be glued next to the side of the cabinet close to the inside edge of the door. The purpose of this is so that the lever on the switch is pressed down when the door is closed, it will turn on the fan and off the LED's and vice versa for when the door is open.
The wires going to and from each component can prove to be troublesome. I suggest you glue them to the sides of the cabinet in neat organized lines, you can even paint them black to hide them. As for the USB plug you can simply lead it to the USB port on the system and plug it in. Make sure you measure out all the wire you need before soldering it all together, as you don't want to come short and have to make more connections.
Step 3: The Circuit
Follow this diagram on how to wire up your own XBOX Cooling System. Please note that this circuit is designed for use in a cabinet with a door so that if the door is closed the fan will turn on & the lights will turn off, and if it is open the lights will turn on and the fan will turn off.
Step 4: Putting It All Togther
This is where the fun starts. Chose a corner for where all your connections will meet (Ex: USB power, Fan wires, LED's, etc.). Then once that place is found check if all other wires can reach their place easily; so see if the LED's can reach the front of the cabinet and if the fan can reach the hole you drilled for it. Because my cabinet had a bit of a ledge inside, I had to use a scrap piece of wood to keep the LED's and switch level with the top of the door. I would suggest that you check your cabinet and be sure a small issue like this doesn't get in your way. Once you have checked all of this its time to glue/nail it all down. I used No more Nails for this simply because its strong, durable, and wont cause any short circuits. After the glue has dried or your finished nailing, double check your circuit to see if its still functioning, if so congratulations! You are finished!
Step 5: Testing, Testing, 1, 2, 3...
Now for the moment of truth. Turn on your system and see if the LED's light up with the door open, then close the door and listen, or look at the back of the cabinet for the fans turning on. If there is a problem double check your circuit and solder connections; however if the problem persists leave a message and I will try to answer it ASAP. Thanks for reading this instructable and the best of luck in your future projects! a full video of my system can be sen below.