As is stated here by others*and i wish i had read this before i bought it!* HD can only be enabled on NTSC US/JAP xboxes, even though my pal xbox will play ntsc us/j no problems *unleashx* it wont produce HD, even though i have the options to do so, 780p/1080i etc...however there is a fix for this if you can be bothered reading some walkthroughs and downloading a patch from various xbox1 forums/sites.
Now after reading the above your probably wondering why on earth i rate it highly then?...i rate it so because even with no HD the clarity/sharpness/ and detail are improved a good amount. The problem with these new HD tellys is they are great for PS3, 360 etc, but if you try to play anything older with no HDMI connections and using the standard AV cable, the picture and sharpness is not good at all...oddly, worse than a standard CRT tv *but i guess xbox was made when CRT was the intended host*
So all in all, while im yet to fix my xbox for HD, the improvment in picture on a HD tv makes well worth the price anyway. It was like looking through a misty window using the AV lead.