Now, the good news: I have been able to install Debian Etch for ARM in my Agestar using the instruction in here: http://wiki.dns323.info/howto:install_debian. Of course there are differences in booting, and configuring stuff, but the steps to produce the root file system are the same. I have also managed to write new kernel to the flash (by using dd if=bootpImage of=/dev/mtdblock1), so now my agestar will go directly to Debian when i turned it on.
I will clean up the code, and write the instruction on how to install Debian this weekend.