phpBB has a feature to select all the threads you wish to move and move them all at once. In fact, I believe there is even a "select all" button so you can just deselect the ones you don't want to move, which would be less than those you do.
And I just used phpBB as an example. You could always have installed a new forum at a later date, you know.
There are conVersion tools that can convert various forum database types to be useable in phpBB (most forum scripts have such tools).
[ June 04, 2003, 23:56: Message edited by: Imperator Fyron ]