initrd in Fedora Core 4 and mount problem

[John Que <qwejohn@xxxxxxxxx>]

Hello, 
  I know from RedHat 9 that I have an initrd file ( initrd_x_y_z.img)
under  /boot
which is used in the boot process.
In the past, when I took that initrd file and renamed it to a *.gz
file (since it is in fact a compressed file ) and than ran:

gunzip initrd_x_y_z.img 
mount -o loop initrd_x_y_z tmp
cd tmp
ls 

I saw the contents of initrd.

When I tried the same in Fedora Core 4 /boot//boot/initrd-2.6.11-1.1369_FC4.img 
and tried  mount -o loop initrd-2.6.11-1.1369_FC4 tmp
I got : 
ioctl: LOOP_CLR_FD: Device or resource busy
mount: you must specify the filesystem type

googling did not helped much ; 

Any idea?

Regards,
John