SOLVED: for details see post #15 below.
I am stilling thinking of setting up dualbooting Cacko and Debian/EABI using the sharp bootloader and kexec as described here: http://www.oesf.org/forum/index.php?showtopic=25555
Even though dualbooting Debian and PdaXii works fine, I feel like having the NAND run Cacko so that there are more varieties.
The question is: the internal disk is already partitioned with one big giant partition filled by the Debian rootfs.
The fact is Cacko/Sharp rom require the internal disk to be partitioned in exactly three parts with exact sizes/sectors.
I cannot do this with GParted in Debian because the program can only resize in terms of MBs, not sectors.
fdisk doesn't work here because repartitioning with fdisk will wipe the disk content clean.
Of course there is a straightforward way: just tar up/create a back up image of the Debian rootfs, then use fdisk to repartition the disk, then put the Debian rootfs back in HDD1, and finally install Cacko and set up dualbooting using the method in that thread. Actually this is also what I may do.
But many Debian Z users have already got the whole system working. This method, however simple, is clumsy and not without risks.
So would it be feasible to do it the other way round: tweak Cacko/Sharp rom in such a way that it simply ignores the HDDs part. In principle it seems workable to me, because the files living in the three hdax do not seem to be critical for the system to operate. Everything important is all in the NAND flash.
I have tried to play with /root/etc/rc.d/rc.rofilesys in Cacko by taking away all the instructions to mount the HDDs. But Cacko fails to boot because of something missing in the process (let me skip the details here).
Has someone ever tried to do a similar thing? I would great appreciate if you could share your insights here. Thanks!