I've configured at least 3 HP G5 servers over the last few weeks and I've discovered that they do not like their network cards to be manually set. We generally set the NIC's to 100/ Full but when this is done, they generally refuse to talk efficiently on the LAN.
I've had this with a Allied Telison, a 3Com and a Cisco Switch, so it definitely ain't switch related.
Further on from this....this thing is breaking my heart. I rebooted the server and it was all OK, but a few hours later its back to 55 minutes to copy over 200MB of data, that's about 1Mb transfer rate. Going to check HP site and see if there is a patch or similar.