I doubt this works with IVTV, but it's worth the investigation: http://www.blackmagic-design.com/products/intensity/
Makes for a very neat installation and unencumbered means of capturing your HD cable/HD satellite tuner. Some others are talking about this card's possibilities, but there are a number of obstacles that must be overcome first: http://www.mythtvtalk.com/forum/general/5271-hdmi-capture.html
One step is that ALSA now supports HDMI passthrough in Linux: http://www.ehomeupgrade.com/2009/01/23/linux-gets-hdmi-sound-pass-through-support-via-alsa-and-kernel-2627-x/
Now all we need is a dependable driver for this card in Linux, stable compatibility with IVTV, and a general defeat of HDCP that governs its playback, and we're set! Hopefully we'll get a breakthrough soon...