Long login time following username/password

I've got a lab of XP SP2 machines (all identical computers) on a 2003 server.
Two of the machines take about two minutes from the time the user types in
username/password to the time the desktop appears. Between login and desktop
it's a blank screen with the mouse cursor. It doesn't matter if the machine
is plugged into the network or not, login takes two minutes. Other machines
login very quickly. The slow login machines are fine once they're done
logging in.

I checked DNS settings on the machines and on the server, all are fine. We
are not using roaming profiles (even local administrator login displays the
same delay). I tried setting the "wait for network" setting through group
policy. I don't think it is strictly a domain issue since the machines are
having trouble even with local accounts, but I'm not sure.

Any suggestions?