We have just moved some users to Exchange 2007 (on Windows Server STD 2008 x64 bit), and users accessing via Outlook 2003 on Win XP Pro PCs.
1. I had a new user who cannot login (it keeps prompting for domain userid/password), but the userid and password is correct because the user can login using OWA webmail. I have tried removing and adding back the Exchange account in Outlook (via control panel -> mail ) but get the same results.
2. I had another user who is able to login using Outlook 2003 to the Exchange 2007 mailbox, now after rebooting the email server, he is no longer able to login using Outlook 2003 (it keep prompting for userid and password). User is able to login to Owa webamil using the userid and password.