IpcMemoryCreate: shmget failed

Whenever I start postmaster w/ greater than 64 buffers, I get the following
message:

Starting postgresql service: 010307.17:10:34.877  [1631] IpcMemoryCreate:
shmget failed (Invalid argument) key=5432001, size=2703360, permission=600
This type of error is usually caused by an improper
shared memory or System V IPC semaphore configuration.
For more information, see the FAQ and platform-specific
FAQ's in the source directory pgsql/doc or on our
web site at http://www.postgresql.org.
010307.17:10:34.877  [1631] FATAL 1:  ShmemCreate: cannot create region

I'm starting postmaster w/ this command:
su -l postgres -c '/usr/bin/postmaster -i -S -B 96 -D /var/lib/pgsql/data
-o -F'

I'm running RH Linux 7.0 and Postgress 7.0.2, the value of shmmax is
268435456.

Thanks,
Mike Coffman
Medical University of SC