Apple has released a pair of Ethernet driver updates for Mac OS X 10.3.3 and 10.2.8.
The new software, "provides improved connection stability". The company recommends all users with Xserves or Power Macs with the Apple PCI or PCI-X Ethernet card installed should apply the update.
The driver for Mac OS X 10.3.3 is available here, a 236K download.
The driver for Mac OS X 10.2.8 is available here, a 121K download.