I've recently clenched a 32" samsung 720P HDTV(3 series w/ integrated speakers) from my local Fry's and I HAPPENED to grab a 9800gtx+ with an HDMI adapter as well. The television's NATIVE resolution is 1366 x 768 however, after installing all of the latest drivers setting the native resolution has become literally impossible. the hdmi cable is a male to male and the video card has an hdmi adapter to go on TOP of either of its two DVI slots. I can only set the screen resolution to 800 x 600, 1024 x 768, 1280 x 720, 1600 x 900, and 1920 x 1080 (each of them gives me a blurry and extremely unstatisfying picture). I find this very intriguing because if i just set up the standard dvi cable, i can set up the native resolution easily. PLEASE help me get to the bottom of this, anybody.
Sounds like the PNP feature is not recognizing your display with that adapter, but PnP is working for direct DVI ( PnP = Plug n Play ) just in case you didnt know.

I'd contact the video card MFR support to see if they can provide you with a way to manually override the systems PnP feature to customize it to the correct native res for the HDMI setup with HDMI to DVI