If you draw power from the 4-pin Molex output connector of a PSU, here is the color coding:http://en.wikipedia.org/wiki/Molex
Note that Ground is Black, Yellow is +12 VDC, and Red is +5 VDC - not needed by your app (unless a small load is needed on the +5 VDC line to operate in this non-standard configuration).
A Molex 4-pin often is not wired very heavily - after all, its intended use is for HDD's etc. that use less than 1 amp each. Your friend's system will need more like 13 to 15 amps available. But if you go to the 20-pin output that is supposed to plug into a mobo, the pinout diagram is here:http://pinouts.ru/Power/atxpower_pinout.shtml
Again, Black is Ground, Yellow is +12 VDC., and it is designed for higher currents.
In buying a PSU, remember that not all its output Watts are on the +12 VDC line. For example, I checked a cheap ($25) 180W PSU and its +12VDC line can output only 10A - net enough for your friend's 150W application. Some cheap 250W units with SINGLE 12 VDC rails put out 13A to 16A max, depending on the unit, just barely enough. A DUAL-rail +12VDC PSU probably is NOT what you want because its +12VDC ouput is split, and you may not get enough from one rail to meet your 13 to 15 A requirement.