For what it's worth
I have succeeded to solve my problem with " RAMDISK :Compressed image found at block 0 " error when booting into Fedora Core 1.
I observed that the problem arise if I boot using lilo from Mandrake 9.2 and not if I use boot disk.
In Fedora Core 1 /boot, I have files :
In boot disk I have files :
So I copied those boot disk files into Fedora Core 1 /boot and changed lilo.conf entries to reflect these files. Run /sbin/lilo.
When I reboot into Fedora Core 1 from lilo, I did not get that error anymore. Thank God