1) search (IMG:
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2) Hi-Def (720p) is the resolution 1280*720. SO any screen that can show that or more is "Hi-Def" - i.e. your monitor can display hi-def 720p when connected to the Xbox 360.
3) black lines. you get to choose which resolution to run in and whether you want "standard" (4:3) which will, on your non widescreen set, fill the screen (no black lines). Or you can choose widescreen, which will give you black lines - "letterbox".
Basically you will be fine. plug in the 360 with the VGA adapter, choose standard and 1280*1024 as your resolution and you will get a full screen, non-stretched, non-black barred, hi-def picture.
nah doesnt work like that. on standard you will get the letterbox except on crappy coded games like pgr3 which will stretch ur image. The only way you can get full screen on a 4:3 screen is by stretching the image, it will look beautiful till ur stupid friends come over and point out ur ret is oval. happened to me as i didnt notice it was being stretched, till one of my friends fudge it all up for me and had me going crazy about it.
imo, im starting not to care and use the stretched image since i dont want to covert my 19" into a 17". If i ever get to the point where the game looks nasty stretched, il put the standard 1280x1024 which will enable the letterbox.