I get the same exact behaviour with my Sproggy 2.7 and Epia M9000.
The processor fan and keyboard initialize on power up but the computer never posts.
I removed the memory and disabled all onboard peripherals and get the same result. With a real atx power supply it posts with some error beeps.
The Sproggy powers my P3-933 w/ 512MB RAM just fine. The Epia is suppose to be a low power board, so I find it hard to believe the sproggy is not providing enough power.
I wonder if the power good and ps-on logic lines are causing the problem. The atx spec says that the power supply should not provide any voltage until the ps-on line is held low. Maybe it is confused when it gets power before it tells the power supply it wants it?