Look on the original disks, perhaps there was a driver in a folder for that NIC. Other than that, I'd contact HP and ask them where you get the drivers, I see they're indeed not on the page for that machine.
I did a search and found this:
http://www.drivershq.com/Drivers/XPD...3/Drivers.aspx
Here's a driver pack from HP for that Intel NIC:
http://h20000.www2.hp.com/bizsupport...reg_R1002_USEN