Certain models (most of the important ones like button pads, doors, door frames) don't load their textures in hammer or the model viewer. Instead they load only the purple/black checkerboard, both in the viewer and in game. I downloaded a map from this site (http://forums.thinking.withportals.com/downloads.php?view=detail&df_id=186) and the models didn't load correctly in it either. When I ran the map none of the textures loaded at all, not even the walls.

Tried verifying the game files in Steam and that didn't help.

Door frame loaded in the model viewer:
http://imgur.com/FRfcLPE

Tutorial map loaded in hammer:
http://imgur.com/WAENKqw

Are you using Portal 1 or Portal 2? In portal 2, those models come without materials, and you anyways don't use those. You should look up the Portal 2 stuff.

I knew it was gonna be a simple answer like that. Thanks!

If you still want to use those models (if you like the design better), you can download some skins for them. Look up Portal 2 Collab iii. They have some textures for them but not the same as Portal 1's. (The original textures look strange if you port them over).