Today,I have recompile kernel 2.6.24 with reiserfs support with Module on rhel5.then I make following change:
1:change /etc/fstab:
/dev/Vg1/lv.root / reiserfs defaults 1 1
and cd /boot/; mkinitrd --with=reiserfs initrd-reiserfs-2.6.24.img. 2.6.24
2:then I use other support reiserfs os enter rescue mode.
commands:
mkdir /source;lvm vgchange -a y Vg1;mount /dev/Vg1/lv.root /source;mkdir /backup;mount /dev/sda6 /backup;
cd /source;tar cvzf /backup/rhel5.tgz *;umount /source;
mkreiserfs /dev/Vg1/lv.root;mount /dev/Vg1/lv.root /source;
cd /source;tar xvzf /backup/rhel5.tgz.then reboot with 2.6.24.

Problem:
VFS:Can't find ext3 filesystem on dev dm-0
mount:error mounting /dev/root on /sysroot as ext3:Invalid argument
setuproot:moving /dev failed:no such file or directory
setuproot:error mounting /proc:no such file or direcotry
setuproot:.......
.............!!!!
kernel panic-not sysncing:Attempted to kill init!

Please help me???
Thanks!!!

the / filesystem, to the best of my knowledge, cannot be reiserfs. You must have an ext2 or ext3 filesystem for /. After that, if you have other partitions declared, they can be reiserfs.

The reason is, in order to read a reiserfs filesystem, the OS has to load the reiserfs module. If the module is stored in a reiserfs filesystem, along with everything else, the OS will not boot.