Well I'm pretty sure I'll need one because I'm used to having my system silent. It's a HTPC as well and the graphics card it has now is an X300 which doesn't have a fan. When I get the 7900GT, I will be able to notice it so I want to get a silencer.
Take it like a man and live with the noise, my PC sounds like a blowdrier when I turn fans on max and run games. I'd just keep whatever heatsink the put on it, quieter often means worse.
you can buy a cheap water cooling from ebay.com.au... just get a Zalman Water Cooling... it's **** cool becoz it's a external water cooling... but the size is big.. but it's quite good for your pc if u wan to silent your noise...