Maybe it should be easier to get to a page number but...
Go to a forum you want to look for old posts in. Notice the link in your address bar. Change the page number to the page you want to see.
In the case of this forum
gets you to January first 2009.
or you can do a Google search like this
The bold part tells Google which forum to look in (1034 is this forum) the 2009 part returns posts from 2009. Add your search terms with the 2009 and you will get posts from 2009 with your other search terms.