New HTPC build

I'm going to build a new mATX HTPC for use in both WXP and Linux. It needs to play 1080p H.264 smoothly and be quiet.

I bought a case already thanks to this thread.
Mobo/CPU/Video/Audio:
It seems the latest crop of on-board video cards are not too bad for HD video playback, with AMD's 780G better than Nvidia's 8x00 chipesets in this respect. However, there is no hardware acceleration for HW decoding in Linux for AMD so far, while Nvidia has VDPAU.
So I'm looking at this combo on newegg.
Edit 7/16: Now I'm leaning towards the new Athlon II x2 Regor 250, an AM3 socket CPU but the M3N78-EM board also support it, sans DDR3 support. I'll probably buy the CPU from newegg (update 7/17/09, bought with coupon AMD791 for $10 off) and buy the board from ewiz (update 7/17/09: bought).

HS: I'll probably buy this one from svc.com which is a little cheaper than newegg and can be picked up locally. The fan needs to be removed and the case vent and fan will be used to force air through the HS. The case fan can be connected to CPU fan header for control.

RAM: (update 7/17/09: bought this one)

HDD: maybe reuse some old drive laying around.

OS: I'll try Ubuntu first.
Media frontend: try XBMC first, Mythtv if XBMC isn't enough.