Depends on how the textures are stored:
If your 3D model uses bitmaps for the texture then they will import, provided the software you are using to create your 3D PDF supports that feature.
If the textures are procedural (tiles, noise functions, etc.) they will not, and you must render them out as bitmaps from whatever application you are using to build the 3D model, then re-apply the bitmap versions to the materials before conversion to PDF.
If you can still get hold of it you can use the Acrobat 8 3D-Toolkit for importing 3D-files and assigning textures. It can handle various file-formats. You can then export your file as u3d with all textures embedded. If you can't get Toolkit, you might think about getting DeepExploration (by RightHemisphere) , which is kind of an extended version of toolkit. But that would be very expensive for just messing around a bit.