Incompatibilities between Gigabit Ethernet PCI cards and Power Mac G5?

Hi, we recently bought a Digicom [url=http://www.digicom.it/digisit/prodotti.nsf/ENProdottiIDX/PCIlangiga32?OpenDocument]PCI LAN GIGA32[/url] Ethernet card to upgrade our [url=http://www.apple-history.com/?page=gallery&model=g5]Power Mac G5 1.8GHz[/url] server. The OS on the G5 is Mac OS X Server 10.4.8 (8L127). The issue is simple: the PCI card is recognized by the system (it appears in System Profiler and as a new port in System Preference's Network pane) but Mac OS X cannot properly use it. We tried to connect the card to a Gigabit switch but nothing happened: no led denoting the connection speed turned on on the switch and the Network Status view in the System Preference's Network pane still show the red light with the "No cable connected" message. We noticed this message in system.log: [code]Oct 31 15:17:28 jedi kernel[0]: AppleRTL8169Ethernet: phyWaitForAutoNegotiation TIMEOUT[/code] So we tried to manually set the Ethernet speed for the card and indeed it reacted, but we managed to have it working only at 10 Mbps (10baseTX). It seems that [url=file://localhost/System/Library/Extensions/IONetworkingFamily.kext/Contents/PlugIns/AppleRTL8169Ethernet.kext]AppleRTL8169Ethernet.kext[/url] is used by Mac OS X to control Ethernet cards featuring the Realtek 8169 chipset but it cannot properly communicate with Digicom's card. The weird thing is that we tried the same card on a Power Mac G4 and it worked flawlessy. Maybe the issue depens on the PCI-X slots available on the Power Mac G5? Are there any other report of incompatibilites between Ethernet PCI cards with Realtek chipsets and Power Mac G5? BTW, we noted that the card's vendor doesn't certify the card for Macintosh systems but we didn't manage to find a PCI Gigabit Ethernet card certified to work with Mac OS X and Power Mac G5 hardware. Could you point me to some PCI Gigabit Ethernet cards proven to work with a Power Mac G5 machine?