i manged to find a zipped debian-final.img.ext2 file online. since the internal memory is very small. i tried remove mapdata(s) and copied it from my PC to N810. The first time I pasted the file. It said the debian.img is missing...sigh...weird. and now I tried the second time, the copy and paste is completed.
Honestly, not just filed two in a row, I have tried for two days.......
anyway, I'll see if this debian-final.img from other source works or not.

I have used Win OS for years but I don't have a single clue about Linux...man...if I could get this work, I'll buy myself a XXXXLarge TimHortons coffee for today !!!!!