sigh....now...I have the debian-final.img.ext2 placed in teh internal memory card MMC2 (as what I could see in the beginning). Now..when I clicked on "set debian HW keys" just to give it a try to see what applications I could use, it shows me the message of "mount failure...debian-final.img.ext2 failed to mount on loop1..."
then i see there's a file called easy-chroot used to mount and chroot into images/partitions and it's already installed on my N810.
sigh......could I return this N810 ?!?!?