[CentOS] ethtool

We've just moved one a new server from our sever room, where I built it,
to the datacenter. We want to force autoneg off, and tell it gigabit and
full duplex. Using ethtool, I get no errors setting the speed or duplex.
HOWEVER, autoneg on works... and autoneg off utterly refuses to work, and
gives:
ethtool -s eth0 autoneg off
Cannot set new settings: Invalid argument
  not setting autoneg

We're on the most current update of CentOS (ok, last kernel, that will
come up on the reboot I'll do shortly), and it's a  Broadcom Corporation
NetXtreme II BCM5716 Gigabit Ethernet

Anyone have an idea what's going on here?

        mark