Yeah I think I've found the problem.

Although I had the part selected then hit "Edit Vertices" I didn't actually select any verts before hitting the "Assign To Bone" button.
I've just realized this and rushed back here in hope that I could post the discovery before you replied. lol

Cheers bud, I'm sure it will work after I go through all parts with the verts actually selected. (step 4.5) lol