I want to build a MythTV back end. I don't want to compile things if I can help it, and I'd like to know what hardware will work with the cable system in the US. Are there any guides to building a MythTV box? I've found several but they all appear to be three or so years out of date and I have no clue how Linux hardware support has changed since then.
For what it's worth, here is a page from my personal wiki that describes two MythTV builds: one that was commissioned by a friend of mine, and one I did for myself. The page is annotated with my thought processes, problems that I ran across (and how I solved them), etc. I also have linked from that page a presentation I gave to our local Linux Users Group on this topic. Perhaps you'll find it helpful.
EDIT: I'd also like to second the recommendation made earlier for Mythbuntu. That's the distro I ended up going with, and the setup was simple and relatively painless.
I would suggest using one of the prebuilt distributions that are specially built around mythtv. There are many and each have their own instruction manuals.
As far as hardware wise, Linux support has grown in the last few years. Any popular distribution should work with most hardware right from the base installation. There are lists of tv tuner cards that work with mythtv if you search around.
Here's my current MythTV set-up:
For the US cable system I prefer cable that doesn't require a decoder box. If your cable requires a box then you'll have to buy/make something to let MythTV change the channel on the box and you'll be restricted to recording/watching one channel at a time (unless you can get multiple boxes).
My experience with the 350 has been okay. Having it output to a standard TV well is difficult. You can avoid that with a modern TV that accepts VGA-in so all your video comes from a graphics card.
It looks like HD video support is working its way towards Linux, but I do not have any experience with that hardware.
Some of the guides get into a lot of detail on how you partition your harddrive. There is a quantifiable performance difference with the file systems. But if you don't notice than it doesn't matter.
Tonight I plan on hooking a wireless bridge to by Myth box. I've had some bad experiences with Linux and PCI wireless cards; I'm avoiding that with the Ethernet to wireless bridge.
Bottomline: Hauppauge SD card(s) with a modern processor, decent RAM, a modern harddrive, motherboard with an Intel GMA graphics chipset and networking that Linux recognizes will be more than enough for a MythTV backend. The default Mythbuntu set-up is working fine for me.