What was special about the password protected forum that would cause a hacker to leave it alone?
To try answer your questions:
1) Highly improbably. Unless you or your host a backup copy.
2) Your host's control panel should offer some means of changing the folder and file permissions. It's a matter of setting the anonymous web user account (IUSR_<servername>), to "read-only" permissions.
I think the MDB needs to be in a folder that the anonymous user can read and write. Hopefully someone will correct me if I'm wrong, but I would suggest you test it yourself. The anonymous user must be able to create, read from and write to the .ldb file, as well as read and write on the .mdb. So, I would put that file in a folder by itself with special permissions unique to that file. With the exception of the "uploads" folder and the mdb folder, there's no reason the rest of the forum (or your entire site) should have anything other than read-only.
You could also put the mdb in a folder above the wwwroot, but your host may not allow that.