There are a few cards that can display HD when used with a DTV tuner and software, ATI is producing a DVI> component video adapter that will connect to your HDTV through YPbPr and will support HDTV 480i, 480p, 720p and 1080i. It was supposed to be available Q1 2002, I notice their site now says "available 2002" so who knows.
There are also VGA>component adapters available now priced at around $300.