Update: Drivers are included in vSphere 4.1.
Download the ISO with drivers from HERE.
Burn to a CD and insert in the drive. Logon to the console as root and mount:
mount /dev/cdrom /mnt
Browse to /mnt and find the file “INT-intel-lad-ddk-igb-220.127.116.11.1-offline_bundle-185976.zip”
Install the driver:
esxupdate --bundle=INT-intel-lad-ddk-igb-18.104.22.168.1-offline_bundle-185976.zip update