Networking problems - if not bad NIC's, the what?

I have a P4, 2.67 workstation running XP Pro, SP2 that is having
networking problems. The user was complaining that it seemed to be
running slowly when using our accounting application.

This PC has a built in Realtec 10/100 NIC card and also has an Intel
Pro/1000 Nic card added in. Both NICs are Not plugged into the network
at the same time - only one is at a time, so the other deactivates.

As a base line, I can ping my PDC from any other workstation using the
"-l 65500" switch and it takes 2ms for the reply. On this workstation,
it takes 11ms. It does this for either NIC card.

I have physically moved this PC to another building so that it's using
an entirly different topology and it still happens. So I know it's got
to be something with the PC.

The NIC's are set to DHCP and all other settings seem to me the defaults
and to my knowledge have not been altered.

I have updated the NIC drivers for both.

I could understand if one or the other NIC card was jsut "bad" and I got
these results, but I find it unlikely that both would be bad at the same
time which makes me thing it's got to be something else - other hardware
- the MB, the OS????

Anybody got any ideas or suggestions?

Thanks,
Mike