Archiving old topics/posts

Not sure if I'm asking this in the right place, or even if it's possible, but...

I've got a board with some quite old posts -- five years or more. It's a fairly active board, and the DB size is just huge. The powers that be do not want to throw away those old posts, but we'd like to reduce the load on the DB.

So... is there some way to archive them? Maybe move them to another table that's searched and handled separately from the regular board?