Using the “Printer-Friendly” button will help with the formatting, particularly if text is being printed off the far right-hand side of the page. (See the button at the top of this, and every other, screen which looks like a printer).
However if the problem is that forum posts are printed in a way where one ends the next begins, as opposed to being printed one to a page, then it’s not an error – the site was designed this way.