a standard Cat5e or Cat6 cable is all it takes.
The Proper WayUsually, the two connectors on the end of an Ethernet cable are exactly the same; data travels through a pin and comes out the same pin on the opposite end. While this is fine for routers and switches, it doesn't work so well for two networked machines — both of which will try to send data down the same line. To allow data to be sent and received successfully, the internal wiring must be crossed.
With this in mind, converting a traditional length of Cat5e or Cat6 cabling into a crossover-capable wire is easy with the right tools. For this you'll need a crimper and some spare RJ45 connectors. Cut off the plastic connector on one end of the cable, and strip back the outer insulation to reveal the twisted pairs within. After flattening out each wire, you should be able to lay them out in the following order:
here). The trick is reordering the twisted pairs so that that they are now crossed. Reorder the cables so that they look something like this:
The Quick and Dirty Way
To start, you'll need to cut off the end of the cable, though giving yourself lots of wire room to work with. The goal here isn't to rewire a new connector, but the cable itself, physically crossing the wires at the point you've cut. Just be warned that this approach isn't at all sanctioned by Category 5 or 6 specifications, and could be subject to interference, poor performance or other problems. However, if you're in a pinch, this approach should work just as if you'd made a proper crimped cable.
With one end, arrange the twisted pairs to appear as they do in the first diagram. With the other, follow the layout depicted in the second diagram. The trick here is to connect these wires together, creating a crossover point midway along the cable. You'll need to be careful when stripping and soldering the tiny wires together, but if successful, you'll have a decent, temporary cable that should just fine.
Images via Flickr users Meu23, Unclebumpy, and The Internet Center.