I'm using Mozilla. (... so Netscape 7 should have the same problem.)
Mozilla's being kinda odd in its handling of this situation, but so is UBB. Fortunately, it seems Mozilla is being inconsistent: For it to keep the text within a <pre> proportional, requires wrapping the <pre> in a proportional font as well as sprinkling in some <p>'s. So, maybe Mozilla's interpreting of the situation will get fixed sometime.