Darn phil beat me to it! :)

...anyway, what PhilC said or my rather more long winded version.

well you can't "weld" per se from Poser unless the .obj was of one piece, cut into two (say in a modeler) with identical vertices occupying the same space in the two pieces where it was cut. If this is the case you would export the 2 objects from poser via the export wavefront object hierarchy, uncheck the universe, check the two objects, export .obj, reimport with weld identical vertices.

I'm thinking perhaps what you want to do is glue the object together via export. File/ export/ wavefront object/ single frame/click universe check box (this deselects all objects in the scene)/ check the two objects/ export with include existing groups in polygon groups.

when you reimport the object will be combined into one selectable object and can be transformed, rotated, and translated as one. The object will also have 2 material regions for the parts and have 2 groups for greater flexibility via the group editor.