There is now a tv tuner card made specifically for Linux. Here is a quote from the website:
"The pcHDTVTM HD-2000 Hi Definition Television Card is the first digital television card to be produced especially for the Linux video hobbyist market. Shipped with the open source multimedia player Xine, the card provides a ATSC stream to the Xine mpeg2 decoder and playback."
I also love this quote:
"Currently the HD-2000 is NOT Microsoft compatible and is NOT supported in Windows 98TM, Windows 2000TM or Windows XPTM ."
It says it requires RedHat, but I bet it works with just about any version of Linux.
Look here.