YMMV

Forcing a NIC to negotiate at a certain speed/mode is simple, as long as you have the right tools at hand. After trying 4 different packages in Ubuntu with mixed results, I got a killer combo.

root@coiso:~# ethtool -v
ethtool version 6

ethtool eth0
ethtool -s eth0 speed 1000 autoneg off
ethtool -s eth0 speed 100 autoneg off
ethtool -s eth0 autoneg on