outlook xp and 2000 cannot logon to exchange server 2003 pop3

[jer_hg80]

Hi, We have some clients using Windows 2000 Pro with Office/Outlook 2000 &
XP and they are having issues/inability to logon to our Exchange 2003 server.
They have 1 new system running Windows XP Pro with Office/Outlook 2003 which
works fine.

Our Exchange server does not allow anonomous authentication on the pop3
virtual server--so we're using "Simple Authentication and Security
Layer/NTLM."

Any ideas on why these legacy versions cannot logon to the Exchange 2003
Server?

Thank you.

Jer