If you already have DoubleMessageBoard but it does not work,
please specify which version (for example "SP v.2") you are using.
Since I don't know the version you are using, I'm not sure...
But I guess you are about to make a new messageboard;
and probably you have the directory permission wrong;
so that the CGI cannot create a file in the directory.
The right permission depends on the hosting company.
But the good guess is permission 0777 works for the
directory where you are going to have a messageboard.
If your hosting company uses special permission
other than 0777, most probably the right permission
is announced somewhere on the company's homepage.
For your 2nd question:
Once you make a new messageboard, that is once you clear
the 1st question, you can access the messageboard directly.
I hope the above advices work; if not, let me know.