Setting up outlook 2003 in vista - smtp not recog user/pw?

I'm using Mail Plus, and trying to configure Outlook. Running Vista Home Premium with Office 2003 SP2. Trying to figure out why the Incoming Server (i.e. POP) isn't found, or my user/pw isn't recognized by the server. Outgoing (SMTP) seems to be working fine. I've tried creating the account a number of times, tried changing the configs, still no luck. All my other internet e-mail accounts are working fine -- it's only my Y! e-mail that is problematic.