I have created a new mesh for a head in a 3d modeling package and would like to attach it to M3's body.   I import the mesh as an OBJ and it comes in gigantic.   Is there a way to scale it done and then how does one go about attaching it to the body?   

Poser's 'scale' is waaay off from most other programs. You have to import it at anywhere from 30-10% (mainly to taste). When you import, one of the items is 'percent of normal size' .

similarly, if you ever export anything out..you'll have to zoom in..;)

Now attaching to the body..I dunno. You could simply 'scoot' it arround on x,y,z axes until it lines up (I do that a lot with hair..;) but actually merging it onto a model would require messing with the mesh itself, which would be tedious, and if you mess up the original mesh, you've messed up Mike. (Best make a copy and save under another name first).

What you might want to try as an alternative, is to just export the head itself into your modeling program.  Move polygons, lines, or points to get what you want, and then save it as a morph (Look for Doc Geep's tutorial on it, should be at the top of the Wings forum logo). That way you don't have to mess with the mesh, and you have a morph target you can use, or share, as you like.