HTPC or simply a PC for the living room

Hi!

I'm thinking about building a PC for the living room, basically for
watching DVD/TV and listening to music:

* Playing music; WMA, mp3, FM radio, Internet streaming radio using
traditional 2-channel stereo into an existing amplifier/loudspeakers
* Playing DVD using the same audio setup plus a PC flat screen
* Watching slideshows
* Watching TV
* Recording TV on HDD
* Casual surfing

Interfaces
* WiFi to existing WinXP server where most files will be stored/backed
up; any ripping would be done here aswell
* WiFi to internet broadband gateway/router
* FM radio in
* CATV/Digital in
* CD/DVD player internal
* USB
* Memory-media
* x.1 audio out configurable to 2.0
* Wireless remote/keyboard
* xx" PC TFT monitor

Priorities
* Low noise/silence
* Nice, modern design
* Small/resonable footprint
* Convenient handling with remote & keyboard
* Set and forget operation :-)

Since the low noise-requirement is quite important to me it sounds
resonable to start off with a system with a low power requirement -
meaning slower clock; question is just how slow can you go and still
have a useful system? I'm looking at the mini-ITX stuff but have no
experience of the VIA processors and their actual performance in
relation to what I want to do with the system. Any advice? Could you
have passive/heatpipe cooling on these? Or ATX and mainstream
processors like AMD/Intel? Possibly sounds like a safer bet in terms of
upgrades? What about the mobile ones for lower power/less cooling
requirements?

OS? Is there a choise? I would love to hear that there is a Linux
distro that without weeks of work would let me do what I want :-).
Perfect if I could boot it over the network from the server :-)