Okay, thought some of you may be interested in this. It turned out to be a really fun project, and I learned a lot about hardware/Linux/drivers etc.
Hardware:
MicroATX motherboard and case
AMD Athlon XP 2500+
Hauppauge PVR-350 capture card
512 MB RAM
120 GB HDD
Old DVD-RW from the closet
Software:
Fedora Core 3 Linux
MythTV
FC3 installed very easily - I just burned the DVD and it booted right up and installed. I followed the
Fedora MythTV HOWTO website, which was extremely helpful in this. I got the OS installed, and used apt-get to do the updates, and install MythTV, ivtv (video card driver), lircd (IR remote sensor driver) and sound drivers.
I initially figured I'd use the PVR-350's video out (kill 2 birds right?) and setup was a bit of a pain, especially getting X to run from there (have the machine's desktop on the TV), but it got going after a couple hours. MythTV configuration is straightforward, as is lircd. (especially with the step-by-step on that website)
So, the machine failed after this - after a bunch of troubleshooting, it was bad RAM - so that was replaced and I was back in business, but then the power supply blew out. Turns out the stock 250W supply that came with the case wasn't sufficient. I found a reasonable 330W micro-ATX supply (which wasn't easy) and now it works like a charm...
Live TV and recording and time-shifting TV works great, but I couldn't get mplayer to play to the PVR-350's video out. I learned that this output is simply a framebuffer, and with the current drivers is not sufficient for playing decoded video to. So I've ordered an Nvidia FX5200 with TV-out, which will work much better for displaying TV and video files.
The interface is quite nice, especially with one of the nicer themes. Its functionality equals Tivo on the timeshifting and live-TV aspect, and rivals it with its integration of videos, music, pictures, etc. It also has built-in transcoder frontends so DVDs can be backed up and added to the library easily.
So, I'll update back if anybody's interested how it works once I get the new video card added.