Why a HTPC?
Why not WDTvLive? http://www.wdc.com/en/products/products.aspx?id=330
or Roku http://shop.roku.com/
I have a WDTvLive, plays from attatched usb storage. network shares. or DNLA server. Youtube + Netflix, can attatch usb keyboard, or use keyboard in remote App on tablet\smart phone.