Yes, I do have the radeon.ko file in the folder structure you indicated, and here's what the console window shows:
sh-3.00# depmod
sh-3.00# modprobe radeon
WARNING: Error inserting drm (/lib/modules/2.6.18.1/kernel/drivers/char/drm/drm.ko): Unknown symbol in module, or unknown parameter (see dmesg)
FATAL: Error inserting radeon (/lib/modules/2.6.18.1/kernel/drivers/char/drm/radeon.ko): Unknown symbol in module, or unknown parameter (see dmesg)
sh-3.00#