Thats an odd request - isn't Shade the same kind of mid-level, all in one app as Carrara?
I've only ever used Shade 7LE and I didn't think very much of it, so I don't know what v8 has.

Anyway you'll have to export your models out of Shade as .obj, .3ds, .dxf, .lwo to name a few, obj files are probably your best bet - they seem to be the most used 3D file format out there. I haven't seen any options for bringing actual Shade scenes into Carrara. If Shade 8 has the ability to bake/convert any procedural textures you've created to bitmaps that will also speed up the process of bringing stuff over.

Hope thats useful.