Bijouchat, you're right - if you want to use the original texture, you can't make gross alterations in the mesh, which probably includes converting a facet mesh to a vertex object. If I recall right, that operation increases the polygon count.
But try importing as a vertex object; that should allow you to retain textures and go into the modelling room. I've noticed that Carrara is compliant in that minor changes to a mesh will not destroy the mapping, but major alterations will destroy the correspondence of the UV coordinates, and the object will then turn black in the texture room.