Given that its a simple machine forum install, the answers would be in the code for it... so I looked there.
Assuming they are using MYSQL as the database and the admin pane allows it:
Looking at the source code for the forum, the posting limits for both normal messages and personal messages is 64 Kilobytes (64*1024*1024) or 67,108,864 characters.
The "subject" or "thread title" size limit on such messages is only 255 characters max, btw.
For polls, the max question or choice size is also 255 characters, for both the poll answers you can pick and the initial poll question you can ask.
EDIT: I cant seem to start new threads at all on the forum, do the admins know that? Is this everybody with a new account or just me?