tyan 2875 and dual opteron 250s

I am using a tyan 2875 with dual opteron 250s for my file server.
I am using the native intel gigabit NIC on the motherboard. I have
a WD 740GD SATA drive, a WD 800JB PATA drive and a
WD 2000JB PATA drive attached to this pc. I am running
Windows XP SP2 on this pc (and with 2 GB ram).

I am having networking timeout issues with this pc from my pc
when under a moderate load.

I am also having problems with the networking locking up when I
try to copy the hardrives to a USB external hard drive.

Does anyone have any suggestions to improve the reliability
of this pc ? I am thinking about putting an Intel NIC into it.

Thanks,
Lynn