Update : nuked all the scene, made a new one, appended all the object, still the same problem. Impossible to get the texture to appear on the object. On the other hand a cube unwrapped and assigned a UV grid appear perfectly textured.
Exported the problematic object as an OBJ and reimported it. Texture works. I’m starting to freak out…
Is it possible that meshes from 2.49 have a problem with UV in blender 2.5?