And I already have a suitable HDMI cable. I bought it (and a DVI adapter) before I discovered that my TV (Samsung LE32BD41) doesn't accept DVI input. I went back to VGA over D-SUB.
Can you refresh our memories on that one?
I use an HDMI cable to feed from the DVI-D port of the MythTV box (with a DVI-D to HDMI adapter dongle) into an HDMI port of our HDTV (Viewsonic).
Mind you, the picture is indistinguishable from the same setup using VGA, but I just feel better about a digital connection there for some reason.

With the new NVidia (ASUS) 8400GS video card, this digital connection stopped working nicely --> the screen showed magenta tones instead of black/gray tones. Peculiar that.
Turns out the BIOS on the new video card seems to think it's using a dual-link DVI-D connection for some reason, even though (1) the card is supposedly incapable of it, and (2) the HDMI input on the HDTV is also incapable of it.
To "fix" this, I collected the EDID info from the VGA port of the TV, and then fed that back to the NVidia graphics driver for the DVI-D port. Problem solved.
Cheers