I tried to reproduce this on my own copy of Windows Vista but I cannot reproduce it - it works properly over here (downloads list of newsgroups and posts properly). I must note that I'm doing all the testing on clean-installed Windows Vista without any additional programs added (this is how we do all of our testing to avoid conflicts with any additional programs). Furthermore, it works well on Windows XP too.
If it connects on port 119 then this is most probably standard non-SSL connection (very few servers have SSL on port 119, usually port 563 is used for SSL - note that Easy Post 2.5 does not support SSL yet because it is quite rare for the news servers but regardless of that, next version will).
I find it strange that Easy Post won't work while all other programs work - it doesn't use any particular unusual command that other programs don't use - in fact if Outlook Express or Windows Mail can connect then Easy Post should do it as well as it uses nearly identical commands as these except it uses yEnc as posting encoding.
Maybe there is still something installed on your computer that blocks this? Common programs that can block other programs are antivirus sofware, antispyware software, privacy protection software and firewalls.
Maybe it is the news server you use? Can you try with some other news server?