On our office network we have a zonenet small office 24 port switch.
Two of the computers could not get a DHCP address and a static ip
address and related info would not work either. The two systems were
running Win 2K/XP and were Dell Precision 4100's. The details follow:

1) The systems could not get a DHCP address to connect to the network.
2) With static IP information the systems were not able to access the
network.
2) With the same network cable, port, etc. another system was able to
get a DHCP address and access the network.
4) From a different known good cable, switch port, etc. the two
systems were not able to access the internet via DHCP or static
information.
5) From my house, on a different home network, the systems were able
to receive tcp/ip information and access the internet with the same
nic card that was used in the office.
6) At my house I ran virus scans and trojan scans and spyware scans
and repaired where needed.
7) When I took the systems back to the office they would not access
the network via dhcp or static info.
8) The only thing that allowed them to get on the network was to
install a new nic in each system. This allowed them to get online
with DHCP information from the exact same network cable, port, etc..
where it was not functioning before.

This makes me think that this issue is somehow MAC address related but
I do not see how. My DHCP server does not show anything strange or
inaccurate and my switch does not have a way to block MAC addresses.

Any ideas as to what could be causing this problem because I feel as
if I worked around the problem but have not completely resolved it and
I fear that the same thing may happen again.

All help is needed and appreciated.