Well, tonights experiment has shown that a 1GHz Via EPIA-M motherboard with 512MB RAM/200GB IDE HD isn't quite fast enough to run MythTV with a USB2 DVB-T stick on a 1280x768 screen. It's close, but there are too many noticeable wibbles in the display. Stock Debian etch install with MythTV packages from http://www.debian-multimedia.org/. Back to VDR it is, until I get round to buying a Core 2 Duo based box.
Speaking of which, does anyone have any recommendations for a HTPC case? I currently have a Silverstone LC02, which is nice but I'd need a new riser card to cope with a ADD2 DVI card and a bit more room internally would be nice. I'd love an Antec Fusion but it's just slightly too wide to fit into my TV unit. The Silverstone GD01 looks pretty good, but is about twice the price of the Antec. sigh.