An Acronym for High Definition Television.
HDTV is from what i can tell from a few hours of surfing the net, a VGA signal, but at screwed up* refresh and resolution
NOTE - I am in the process of trying the below, i havent done it, im just processing information i find on various websites and trying to put it all in one place for people to use.
there is lots of information, the most useful listed below
How to use powerstrip to make you PC output friendly HDTV signal http://www.digitalconnection.com/Support/cliffnotes_17.htm
It has listed a lot of settings you may need to set your computer to connect it using HDTV to your TV.
also check out http://www.digitalconnection.com/FAQ/HDTV_10.asp
a ready made xconfig file for an nvidia svideo output is available at http://wilsonet.com/mythtv/XF86Config-HD.txt http://wilsonet.com/mythtv/mythhd.php
this will let you do 960x540p or 1920x540p i gather to change the overscan settings to adjust the borders on the display you can adjust the timings in very small increments
One page links to HDTV: