doubtful, unless you're very lucky and have the correct pinouts miraculously the same as the 20 pin. Not all of those pins are power, you see, and if.. say, you mix the power and ground power/nuetral and put it backwards, you're probably gonna be in for a nice little fireworks display. PLUS, you are now messing with the possibility of energizing the entire case giving you a nice little shock when touching it. In short, I wouldn't recomend doing it. May hurt yourself, cause a small electrical fire, or if you're lucky just a small puff of smoke. Then again you may have a chance in 1000 that the wiring schematics match perfectly.
If you argue with an idiot he will drag you down to his level and beat you with experience.
I am not a fast writer.
I am not a slow writer.
I am a half-fast writer.