I'd highly recommend using one of Shuttle's bare-bones PCs as a starting point. They're small, quiet, and surprisingly upgradeable. For your uses, I'd recommend this one - it has a replaceable DVD drive for when you want to upgrade to Blu-Ray, two internal 3.5" bays for your HDDs, a couple of eSATA bays, two low-profile PCI ports (one vanilla PCI, one X16), and built-in TOSLINK and coaxial digital audio, all running off of a measley 400W PSU that's (in my experience) whisper-quiet.
Just throw in a cheap Core 2 Duo, an equally cheap-ass low-profile graphics card w/HDMI, a stick of RAM, and a hard drive of your choice, and you're good to go.
"'Casual games' are something the 'Game Industry' invented to explain away the Wii success instead of actually listening or looking at what Nintendo did. There is no 'casual strategy' from Nintendo. 'Accessible strategy', yes, but ‘casual gamers’ is just the 'Game Industry''s polite way of saying what they feel: 'retarded gamers'."
-Sean Malstrom
