After over a year of using myth on my laptop (which has tv out) to view video files on tv, I now have an honest-to-god working mythtv setup with dual tuners, remote control and everything.
For my birthday I obtained a DViCO FusionHDTV DVB-T Dual Digital 4, after doing a spot of googling about Linux compatibility. This is a PCI card that, after plugging in, is detected as two USB tuners and an input device.
I had scrounged together a pile of hardware from various defunct machines in the house and been given a mobo by a friend (Thanks Steve!) The system is an Athlon64 2800+ with 512Mb ram, a fanless nvidia FX5200 with an RCA tvout connector and an 80Gb harddisk. (Though all recording is done to a 500GB LVM volume in another room via NFS over 100baseT)