I just searched "box" with the text file open.. could be it's not in the poser 6 ini at all. Typically this issue is caused by video driver issues. Last known best ati drivers are this month's new release, and I believe, Obtober 2007.

No idea when the last best nvidia drivers were released.

(EDIT: I did check, and the boxpicking option wasn't added till poser 7... sorry.)

Way too many people take way too many things way too seriously.