I am experiencing the exact same issue. My nic speed keeps auto negotiating to 100mbps even though it's a 1000mbps card. The switch is also a gb switch. The port is configured exactly the same as all the other ports on the switch. The hardware (HP DL380 G5) is exactly the same hardware as the other vmware hosts plugged into the switch and they're all autonegotiating to 1000mbps. The only difference between those machine and this one is that my other machines are running esxi 3.5 and esx 4.0. This machine, the one I'm having trouble with is running esxi 4.0 update 1 - the HP Proliant specific one.