I'm making slow but steady progress getting Myth and Xen going. Cabled up the spare bedroom yesterday so it's now got a TV aerial port. Plan is to put the computer behind the door fo the spare room, which has quite a bit of space behind it and should fit the machine nicely. The software is the only barrier now, and that's coming along very nicely.
For some reason debootstrap to Ubuntu Edgy ends up with no access to the network. Not sure why. Then if I try Dapper it works fine but has a weird problem with tzconfig trying to write somewhere it shouldn't, so I can't apt-get dist-upgrade to Edgy. I've gone with Debian for dom0 and domU for now, and it works fine.
I've managed to get the domU seeing the USB digital tv stick by hiding the USB PCI card from the dom0 kernel (pciback.hide in the kernel command line) and exporting it into the domU. I'm pretty amazed this worked so easily. That should make adding more tuners pretty easy too.
My only real issue with Xen has been the syntax of the config files. It's not particularly well documented and seems to have changed a few times in the past, which means when you find something online it won't necessarily work in the version you have.
Once I've got Myth settled down, I'll start working on my desktop which will be using one of the thin clients I own. Last Thursday I bought a really nice 19" LCD screen, which will become my desktop screen. Will be nice working on a decent sized screen and a real keyboard again after months with the laptop.