Which are you referring to by old and new? There is Discussions (newest and avaialable at /d), Forum (thread-based like Message Wall, Article Comments, and Blog Comments and available at /wiki/Special:Forum), and wiki-style forums (similar to talk pages and available at /wiki/Forum:Index).
For Forum itself, you should be able to ask for it to be disabled through Special:Contact. Staff seemed to remove it in favor of Discussions, so it shouldn't hurt to try. (Also discussions are available at /f now instead of /d)