Hi,
in my AppleTV every time backrow kiks in, the resolution is switched to 640x480 (i guess since my plasma TV tells me the info "575 i"). After that, if I go to "settings" and set the res. to 1080i HD, the resolution is swiched accordingly and the ATV works well...untill next reboot. More precisely, the hi-def resolution is mantained through the entire boot process but at the end of the intro movie is switched back to 575i.
It seems like there is an 'override' setting in some finder configuration file but I have no clue
My ATV was patched with "ATV USB creator" and worked well for a year.
My last modification to ATV software were updating XBMC/Boxee (using their update process) and moving a Quicktime library out of "Disabled" folder that I found inside /System/Library/.../Quicktime wich caused a black screen (but with audio) during the playback of the Apple Trailers.
I can't remember if any of the above modification caused the problem of the resolution.

Before I reinstall the ATV OS do you have any suggestion to solve the riddle ?

P.S: sorry for my english

Problem solved!
In NitoTV there is an option "Safe screen release" that was checked; that caused the resolution to be forced to 480i every time finder was restarted.