1080i ?

What dictates if a monitor can display 1080i, given the source is indeed 1080i.What is 720p (i understand 720 progressive lines , i mean what source is 720p) ? Why does 420p look better than HD on my data grade NEC projector.I currently line multiply with a dwin transcanner.
HDTV broadcasts are either 1080i or 720p
The monitor itself dictates whether it is capable of displaying a particular format--check the user manual. The number--1080, 720, 420--are the number of scan lines shown. The letter--p or i--says whether the signal is progressive (all scan lines drawn at once) or interlaced (half drawn and then the others filled in). Some videophiles believe 720p looks better than 1080i. Quicke, there is a third HD format that no one supports--1080p--which is supposed to be spectacular.
Many of your questions are answered at projectorcentral.com in an article titled "The Difference Between HDTV, EDTV, and SDTV".

That's why I said "broadcasts."