If you have a new topology that you made in an external app, load the high poly and the new low poly, divide the low poly, then hit the project all button in the subtools palette.
This should give you the result you're looking for.:)
Yeah, when I'm doing that, I make sure that the new mesh you're projecting onto has about the same amount of polygons/subd levels as the original so the shapes/detail carry over well. I also tend to project one Sub D level at a time, working my way up from the lower to the higher, (on both the source mesh and the target). Then there's less of a discrepency between the meshes, and less of a margin of error in projections. That's my theory anyway . I also store a morph target before each projection, so if something does come out kinda whacked out, you can just use the morph brush to get rid of it pretty quick.
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This should give you the result you're looking for.:)
http://www.pixologic.com/docs/index.php/Topology:_Mesh_Editing