Step 1: What You Need
Wire Cutters and Stripper (Scissors will work but it makes it a bit harder)
Electrical tape (Or just plain Scotch-Tape)
Step 2: Cut Up the Headphones
Step 3: Connecting the Wires
To test which wires came from the end prong, I chose a colour, and connected them (I started with black and I connected the black wire from the speaker with the one from the jack), and tested the other wires by connecting the same colour wires together, one at a time, with the end prong plugged into the computer until a headphone came on, which it didn't. So I disconnected the blacks and connected the yellows and tested again. One of the headphones came on when yellow and white were connected, so I left them connected and cut away the two remaining wires coming from the jack.
Then I had to find out which of the two remaining wires coming from the headphones was positive and negative. I connected the black to the whites and the pink to the yellows with no results, so I switched them and the second speaker came on. I twisted the two bundles together.
In the end I had the white from the jack connected to the pink and the white from the headphones, and the yellow from the jack to the yellow and the black from the 'phones. Of course your colours may be different, but if you have Quantas headphones, you don't have to test.