PE1850 does not boot when using initrd image

[Reiner Dassing]

Hello,

I don't know whether I am in the right list, but I will try!

My main question is:
Is it possible to debug initrd scripts during the boot process?
Or, what the hell is wrong with my setup?

I set up PE1850 with Debian/etch and installed the necessary drivers
into the kernel. It boots, I should be happy.

Then I installed Xen3.0.4 which wants to make use of an initrd image to
be as flexible as possible. The drivers are not in the kernel, they
should be loaded as modules.
After trying now for more than a week, the boot process ends up with
Kernel panic - not syncing: VFS: Unable to mount root fs on 
unknown-block(0,0)

The grub/menu.lst has the following entry:
title 		XEN 3.0.4-1 / XenLinux 2.6.16.33
root		(hd0,1)
kernel		/boot/xen-3.0.4-1.gz dom0_mem=196608 console=vga noreboot
module		/boot/vmlinuz-2.6.16.33-xen root=/dev/sda2 ro console=tty0
module		/boot/2.6.16.33-xen-initrd

The initrd image is built by:
mkinitramfs -k -o /boot/2.6.16.33-xen-initrd 2.6.16.33-xen

The modules to be loaded are defined in /etc/initramfs-tools/modules and
they are also loaded into /etc/modules:
scsi_mod
sd_mod
mptbase
mptscsih
mptspi
jbd
mbcache
ext3
reiserfs

(PE1850 uses ext3, the virtual servers are setup to have reiserfs)

I tried a lot of more modules without any success.

Thanks for your time and hint to find a solution!

Regards,
Reiner