FWIW, Sh4's limitations may well serve you alright. No FSAA option, and limited to 1024x768 means that it's just not going to be THAT hard on a video card.
Look into the GeForce 7600GT. No external PCI-E power connector needed, should run on that PSU just fine (they are REALLY low power), and shouldn't have a problem with anything Sh4 *can* throw at it.
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