Here are my experiences building an HTPC with MythTV.
Installation. You can start with a common Linux distro like Fedora or Ubuntu and install MythTV on top of the distro, or you can use a specialized distro like KnoppMyth. As of June ’06 I had trouble finding stable MythTV packages to install or figuring out all the dependencies needed to compile from source. I finally gave up and used KnoppMyth R5C7, which is easiest if you let it take over the machine and delete all other partitions on the boot drive, otherwise you have to know what you are doing with lilo.
Hardware. I have a couple of HDTV tuners: fortunately support for them had been added into the kernel during early ’06, but otherwise I would have been faced with applying kernel patches. Even so, it took me a while to figure out I needed the latest kernel. Decoding HDTV signals takes significant processing power: I have a 2.4GHz Celeron CPU and originally output stuttered badly. Fortunately I had an nVidia video card and selecting the XvMC option allowed the card to assist with MPEG-2 decoding and eliminate the stutter (in MythTV’s frontend menus, navigate to: Setup -> TV Settings -> Playback). To take advantage of the 16:9 aspect ratio of my Sharp Aquos display I had to manually customize my /etc/X11/XF86Config file. I’m not sure I did it right but it seems to work.
Noise. To record and play programs the HTPC has to be left switched on for extended periods of time. Even though I already had a Zalman CPU cooler the whine of the small northbridge cooler drove me to distraction: I had to special order a Zalman northbridge heatsink with an epoxy binding as the motherboard had no mounting holes for anything else. I was able to quieten my disk drive by using ‘hdparm -M128 /dev/hda’ to set its acoustic management feature.
Power. To get my HTPC to power off between recordings I had to figure out how to configure /etc/nvram-wakeup.conf for my motherboard. My motherboard (a FIC Dynasty) did not appear supported and I was unable to get it to work.