LWP is, i'm sure, what you need. I haven't played with it at all, so i can't give specifics but you want to do is something like this:
Visit the message board you want to upload to and read from. Read the HTML source to see what kinds of forms they use and what type of name/value pairs they want. When you figure out what name/value pairs are used, you can simulate those POST and GET actions with LWP, sending from your system rather than the web page.
I hope that helps somewhat..
-Syn0