Wow! Here is a really clear, step-by-step set of instructions on how to make your own network cables:

We live in an increasingly do-it-yourself world. We can check out our own groceries, pump our own gas and diagnose our own — OK, maybe not that last one. But for the do-it-yourself type, making your network cables is no problem. These days, ready-made Cat 5 cables — the standard kind used for most Ethernet networks — are relatively easy to find at most electronics stores at reasonable prices. So why assemble your own network cables? It may not be something you do everyday, but having the supplies and know-how to whip up a network cable on the spot can be very handy.