The X1531 cable
You need the following parts to build this cable:
Step 1. Use a sharp knife to strip off the insulation from about 2/3 of the length of the cable. Seperate the wires into two strands, 2 and 4 wires each. Use heat-shrink insulator material to insulator the two strands again, so in the end your cable represents an Y-fork.
Step 2. Solder the 2 wires of the first strand to pins 1 (+5V) and 4 (GND) of the 15 pin plug.
Step 3. Solder the 4 wires of the second strand to the appropriate pins of the 25 pin plug.
Step 4. Solder the 6 wires on the other end of the cable to the 7-pin mini-DIN connector. Solder the two GND wires from the different plugs together, and add short lengths of wire to connect pins 1-7 and pins 2-5. You should have the following connections:
Source: The Joe Forster-STA homepage