Sorry it took so long, I couldn't use my Construct computer all day yesterday, so I just whipped this up in the last twenty minutes. It seems pretty solid, but I know it could probably be cleaned up a little (especially the centering-on-ladder code, it's a bit redundant having it occur twice). At the very least it should give you an idea of where to go from here.http://www.fileshack.us/get_file.php?id ... ladder.cap
The whole thing's commented, but if you have any questions just ask.
But yeah, everyone posting suggestions in this thread were pretty much on the right track, except I used Set Speed in the Y direction instead of manually setting the Y position (that could cause problems with clipping into solids).