well i wouldnt be using a graphics card in a htpc.
Would get a mobo with hdmi out probably using the new intel g35 chipset which is more than enough. Infact you can underclock the c2d cpus to about 1.6ghz and still get flawless hd playback (think 1.4 is the bare minimum) with the g35 chipset.

As for the ventilation, they seem to have pretty similar ventilation layouts, granted im not to sure about the twin 60mm fans thermaltake use for the exhaust. But then things can be done about that.

I doubt it will ever generate that much heat anyway.
Really id like to compare the two side by side but the chances of that happening are not likely.

Does the zalman use the imon software for its screen or is it its own ?