Don meant the Linux kernel ...
What distro are you two running? RH comes with shmem configured reasonably, you don't need to recompile the kernel to get things up and running (though you do need to if you're to use more than 16MB for the Postgres shared buffer space).
Since you didn't specify "-B" when trying to run the postmaster, it's only asking for 64 blocks of shared memory, a bit over a megabyte. Any kernel with shmem or semaphores configured to a reasonable value should have no problem with this.
So ... try Dan's recompile-the-kernel suggestion.
