Duck and Cover

I went to the gunrunners in boneyard and when I try to leave the guy who stands on the 1x5m Plank won't move.... umm.... what do i do?

Is he stuck in a doorway or something? If so, unfortunately, this was one of the major issues with Fallout 1: NPCs stuck in doorways. Unless they eventually move of their own volition, there's no getting by them unless you kill them.

You did try to talk to him, right?

Should be able to initiate conversation with him outside of "plank" range, which'll make him move. If you talk to him while blocking him from moving off the plank it won't work.

^ This. Also there's a way to get infinite xp here (might only work with v1.0), but ill let you figure out how, hint: it has to do with the quest to clear out the deathclaws.