Hmm.... I'm running out of ideas
You know what I mean by a seperate line don't you?
On modern PSU's, like for example, mine, I have something like 3 wires coming from it, that are power lines, that carry the 12v supply.
What you want, is to find a 2 free lines, and use these JUST to power the graphics card. You don't want to use one line to power both connections, as this won't work.
The other remaining line, can then be plugged up to the remaining sections of the computer, since you don't need much power to power the DVD, etc, etc you may have in the system.