Is there a way to split the viewport so I can view my unsubdivided model in edit mode and my subdivided model in object mode at the same time? I'd like to be able to edit my mesh and see it update on a subdivided version on a separate window. Thanks!
A trick to do that :
Temporary use a mirror (1) with another object as center, here an empty (2).
You can edit the original and see the mirrored mesh with subsurf.
When finished, remove or hide the mirror modifier.
Just remember that the shape is mirrored... so the left becomes the right, etc.
Unfortunately, no there's not a way to do exactly what you're looking for.
There are some workarounds, though. One possibility has been mentioned by Lemon.
Another option is to create another object with a linked mesh. You can do this either by selecting the original and then pressing Alt D. This will make a duplicate object that uses the exact same mesh. In fact, if you change the mesh in one object, it will update in the other. For more information on that, and other methods of doing the same thing, check out the Duplication Section in the Manual.
Once you get them linked, you could remove the Subsurf from one of the objects, and leave it on the other. Then, edit the mesh that doesn't have a Subsurf, and you'll see the changes on the one with Subsurf. You could even go to the point of having two 3D Views, one of them focused on one mesh, and the other focused on the other.
Note: Sometimes updates happen live in edit mode, but sometimes they don't propagate to the other objects until you leave edit mode. Either way, this is probably as close as you can get in Blender.