Thanks for that. We have loaded and successfully forced the load of the ELsmp kernel, but this only shows 8 of the 16 cores present. One of my colleagues has since found a restriction that RHEL 4 U5 can only support 8 cores or CPUs with the ELsmp kernel.
(Taken from http://kbase.redhat.com/faq/FAQ_85_7936.shtm):
The largesmp kernel is required for any AMD64 or Intel EM64T host with more than 8 CPU cores (regardless of how many sockets).
On supported architectures, systems with greater than 8 cpus will get automatically installed with largesmp kernels.
Hence we have to use the 2.6.9-55.ELlargesmp kernel to get all 16 cores in RHEL 4 U5 or use RHEL 5 which has better support for quad core with the standard ELsmp kernel.
Thanks - problem closed