The Inquirer reveals that ATI could launch a Radeon X1900 XTX with HDMI support if its partners chose to implement it.
ATI actually said that you can do HDMI via DVI but mind me that would not be the full HDMI, as it would transfer video only.
The HDMI interface has to conduct audio and video signals and therefore you should make a custom graphic card design with an audio connector on the card. It may sound silly but you actually do need this, otherwise you would be stuck with an HDMI graphic card that will transfer video only, not audio.
You also need one more chip - the famous SiI HDMI transmitter chip, which is actually an HDCP content protection chip, to call your computer HDMI compliant.