* Incredibly slow login

Our environment:
* Server: Netware 6.5 SP3
* WorkStations: Windows 2000, Windows Xp
* Novell Client versions: 4.90 SP2, 4.91 SP1, 4.91 SP2 (doesn't appear to
* DA setup and running - IP address of DA distributed vis DHCP
* slpinfo /d shows the w/station knows about the DA

The User experience:
User types login name + password then clicks OK. They can sometimes wait
for 5 minutes and sometimes much longer before they successfully login.

Other things we have noticed:
* If they logout after a successful login, they have no problems logging in
again - the login is fast.
* If they shutdown, then they have to wait again
* If you change the context and server, then and login as a different
person the logion is fast, followed by fast login as to the original user,
context and server will be fast
* Replacing the server name with the IP address of the server usually
results in speedy login.

Any suggestions gratefully received.