What is 480 I, 576i, 720 p, 1080i, P? What is HDTV?

They are all standard display modes of TVs. I indicates interlace scanning, and P indicates row-by-row scanning.

525 I is a standard ntsc TV display mode with a frequency of 60Hz, 483 vertical scanning lines, visible vertical scanning lines, or, recorded as I or 525i.

576i is a standard pal TV display mode with a 50Hz frequency, 625 vertical scanning lines, 576 visible vertical scanning lines, or, recorded as 576i or 625i.

525 P is the D2 standard digital TV display mode, 60Hz frequency, 480 vertical scanning lines, 525 visible vertical scanning lines, or 16: 9, recorded as P or P. The actual image resolution within the Xbox is 640*480.

750 p is the D4 standard digital TV display mode, 60Hz frequency, 720 vertical scanning lines, 750 visible vertical scanning lines, recorded as P or P. The actual image resolution within the Xbox is 1280*720.

1080i is the D3 standard digital TV display mode, 60Hz frequency, 1125 vertical scanning lines, 1080 visible vertical scanning lines, recorded as 1080i or 1125i. The actual image resolution within the Xbox is 1920*1080.

The HDTV standard is a high quality video signal standard, 720 p, 1080 I, P, but currently supports P, which is also known as support for HDTV.
Because XB games are dominated by 480 P, 720 p, and I, the actual PC CRT resolution is as follows:
480 P = 640*480

720 p = 1280*720 (not 1024*720/1024*768/1280*1024)

1080i = 1920*1080 (display on the interline)