Windows Security and Newsgroups

New laptop with Vista. I'm the admin, only account. Trying to set up
newsgroups from my news server, which requires me to log on. All is set up
OK in the account screens. When I try to initially download the newsgroups
on the server, up pops a Windows security notice, asking me to log on to the
newsgroups server- "verify that both username and password are correct for
your mail server". After I enter user name and password, and click OK, the
screen keeps popping up asking for same prompt. I am giving it the correct
info, but will not accept, so can't begin to download newsgroups. Whatever
I enter will change what's in the account screen for the server setup. Tried
turning all the windows security options off that I could find, but still
can't get past the security screen. Any advice on this?