HDTV (High-Definition televion) as broadcasting of television signals with a higher resolution than traditional formats (NTSC, SECAM, PAL), you can learn here (Wikpedia).
About NBC' broadcasting in high-defition : here (NBC's HDTV in 1080i format)
Canada's CBC has a simple visual explanation pages about HDTV : here
BBC's "What is High Definition television (HD)?" : here
ABC's HDTV FAQ's : here
CBS TV/HDTV SCHEDULE : here
WUSA9's explanation page about HDTV : here
Hitachi Ultravision 26HDL52 26" LCD HDTV
* 26-inch slim-profile LCD TV with integrated bottom speaker design; measures 26 x 18.25 x 4.1 inches (WxHxD)
* Integrated ATSC tuner for over-air HD broadcasts
* 1366 x 768-pixel resolution; 3000:1 contrast ratio; 170-degree viewing angle; 8ms response time
* Connections: 2 composite, 2 S-Video, 2 component, 1 DVI, 1 PC, subwoofer out
* Two stereo speakers, 10 watts apiece (20 watts total); SRS WOW virtual surround sound
Sharp LC-26D4U AQUOS 26" Flat Panel HD-Ready LCD TV
* 26" Widescreen Advanced Super View LCD Panel
* True 16:9 (1366 x 768) Resolution
* Digital Cable Ready with CableCARD slot
* Dynamic Contrast Ratio (4000:1)
* 56.20lbs (LxWxH) 43.50"x 12.04"x 25.46"
Sony KLVS23A10 23" LCD WEGA HD-Ready Flat Panel TV
* 23-inch LCD TV measures 22.4 x 17.6 x 8.6 inches (WxHxD) with included tabletop stand
* 181-channel tuner (NTSC); 16:9 native aspect ratio; side A/V inputs
* CineMotion reverse 3:2 pulldown detection for watching progressive-scan movies in native 24-frame format
* Inputs: 3 composite, 3 S-Video, 1 component, 1 HDMI, 1 VGA
* Two stereo speakers, 5 watts apiece (10 watts total)
Samsung LNS2651D 26" LCD HDTV with Integrated ATSC Tuner
* Stylish 26-inch LCD TV in black with integrated HDTV tuner; measures 26.6 x 20.9 x 8.5 inches (WxHxD) with included stand
* Game Mode optimizes image quality and sound; connect portable digital players and control via remote (with RS232 cable connection)
* 1366 x 768-pixel resolution, 500 cd/m2 brightness, super-fast 8ms response time, 4000:1 contrast ratio, 170-degree viewing angle
* Connections: 2 composite A/V (1 side), 2 S-Video (1 side), 1 component (Y/Pb/Pr), 2 HDMI, 2 RF, 1 USB, 1 RS232
* Two stereo speakers, 5 watts apiece (10 watts total); SRS TruSurround XT virtual surround
Samsung LNS2641D 26" LCD HDTV with Integrated ATSC Tuner
* Powerful entry-level 26-inch LCD TV with integrated HDTV tuner; measures ww x hh x dd inches (WxHxD) with included stand
* 3D Y/C digital comb filter for improved transition detail; picture-in-picture (PIP) capability
* 1366 x 768-pixel resolution, 500 cd/m2 brightness, super-fast 8ms response time, 3000:1 contrast ratio, 170-degree viewing angle
* Connections: 2 composite A/V (1 side), 2 S-Video (1 side), 1 component (Y/Pb/Pr), 2 HDMI, 2 RF, 1 USB, 1 RS232
* Two stereo speakers, 5 watts apiece (10 watts total); SRS TruSurround XT virtual surround
Sony KDL26S2000 26" Bravia Flat Panel LCD HDTV
* High-performance 27-inch LCD TV with integrated HDTV tuner; measures 26 x 20.4 x 8.6 inches (WxHxD) with included stand
* Wide color gamut produces deeper reds, more vivid greens, and cleaner blues; 3D digital comb filter; Cinemotion 3:2 pulldown
* 1366 x 768-pixel resolution, super-fast 8ms response time, 1300:1 contrast ratio
* Connections: 3 composite A/V (1 side), 2 S-Video (1 side), 2 component (Y/Pb/Pr), 1 HDMI, 1 RF
* Two stereo speakers, 10 watts apiece (20 watts total); Dolby Digital decoding and SRS TruSurround XT virtual surround