I will answer you, but not for the GPU, for the CPU. If you get a mini-PC like the Shuttle you should get a P4C 2.8GHz not a P4E 2.8GHz. The P4E is running hotter, need more power and is slower than the P4C.
If you have the money get the X800, it will last you longer than the 9800PRO. And the X800 power requirement and size will not be a problem for your Shuttle MINI-PC.
And I agree that you should get 1Gig of RAM. You might even do some overclocking if you get good DDR466 RAM. Review od the Shuttle : <A HREF="http://www.hardocp.com/article.html?art=NDg3" target="_new">http://www.hardocp.com/article.html?art=NDg3</A>. I nthis review, they achieve 250MHz FSB. So you might expect this from your box too!
AnandTech offer great memory reviews/comparison and sometime it's better to buy good DDR433/DD466 instead of cheap DDR500.
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Lookin' to fill that <font color=blue>GOD</font color=blue> shape hole!