MythTV can offload decoding to the GPU. The Foxconn has an NVidia ION MB which will do 1080P all decoded from the builtin GPU. The same system has Gig-Ethernet and can use up to 4G of RAM. Plug in a USB Mini BT dongle to use a KB/Mouse if you want. The Foxconn can be bought for $200 (£150 in the UK) as a barebones system w RAM although it's hard to find in the UK. There are other manufacturers that do rebranded systems of the same type and it's so small you can mount it on the back of a TV or monitor. Again, if you PXE Boot a MythTV frontend, you don't need a hard drive inside it'll be virtually silent.