Step 1 : Gather Materials
You'll need a few things to build the adapter:

PARTS
-XBox Controller cable or extension
-Junk USB Female connector
TOOLS
-Pocket Knife
-Flathead Screwdriver
-Soldering Iron
-Dremel
-Hot Glue gun

once you've got these, the fun can start

Step 2 Open XBox Plug
We'll need access to the inside of the XBox connector to build the adapter; however, we need to be able to close it again, so be careful.

First, use the knife to cut the cable off the XBox connector and cut the strain relief flush with the plastic casing.

Then, use the Flathead to lever the casing open by inserting it where the wire enters and twisting. It is ok to mar the edge at the end of the casing, as this part will be removed later.

Step 3 Remove Shield and Wires
use the flathead, with help from the knife to remove the upper part of the metal shield.

then, heat your soldering iron and carefully remove each wire without breaking the traces or de-tinning them.

Step 4 Remove USB Connector from Junk Electronics
Disassemble your piece of scrap electronics, and remove the USB connector.

to do so, first lay a piece of desoldering braid across the set of 4 soldered pins that transmit the USB data. Heat the back of the desoldering braid until it is removing the tinning from the soldering iron. Using a pair of tweezers, carefully lift the braid away from each solder pad, while still applying heat.

Next use either a fresh piece of desoldering braid or a desoldering bulb to remove the large legs that hold the usb connector to the board. you will also need to bend the legs outward, just a bit.

apply upward force on the connector, while heating the pads where necessary to break the remaining bonds.

re-tin the leads, and remove any lumps of old, hard solder.

Step 5 Connecting the two
it is relatively well known that XBox controller ports are essentially USB ports, so the connection is simply wire to wire,but the big thing to remember is: skip the pin that had the yellow wire, and don't short it (the yellow wire apparently carries 12 volts.

first, bend all four pins on the USB Connector to face outward from the back of the connector. looking down from the top, bend the left most pin slightly to the left, and the other three pins slightly to the right, to make room for the unused pin.

solder the connectors together, following the diagram

bend the supports and shield, so they form some semblance of structural integrity, and solder them in place.

now here's the secret I didn't learn until late in the process. Short the ground pin to the metal shield of the XBox connector (this corrects lots of connection issues). test your connections before you go any further.

USB PINOUT KEY
1. +5v
2. -DATA
3. +DATA
4. -5v (Ground)

XBOX PINOUT KEY
1. -5v (Ground)
2. +12v (Unused)
3. +DATA
4. -DATA
5. +5v

Step 6 Dremel the Casing
Remove a section of the casing you removed from the controller cable, where the wire entered, so that the USB connector can fit in the old shell.

Also remove the posts from the casing, as they will no longer fit.

Step 7 Glue it all in
I used "Gorilla Glue) which I put under the connector, on the solder, and on the other side. Warning: Gorilla Glue expands, use a good sized dab no larger than ring toenail.

Now you can connect mice, keyboards, and special flash drives that use fatx (look up on google) I made one for my mouse and one for my keyboard, works real well