From the OCFS2 page:
OCFS2 1.6 is only available with the
Unbreakable Enterprise Kernel. Users
wishing to upgrade to the new release
must logon to the Unbreakable Linux
Network (ULN) and subscribe to the
Oracle Linux 5 Latest channel.
Looks like oracle is going to make you convert your kernel to their "new" Unbreakable Enterprise Kernel, or use a vanilla kernel with 1.6 compiled in. From the ocfs2 web page:
The file system source code is
available with the mainline Linux
kernel that can be downloaded from
kernel.org. The file system source
code for the Enterprise kernels is
available from oss.oracle.com.
The ocfs2-tools source is available at http://oss.oracle.com/projects/ocfs2-tools/files/source/v1.6/ (No binaries for rhel5)