Need some quick advice

when i add a lamp to the scene and press p my model has missing sides and faces and such? heres a pic:

whats going on?

Try recalculating face normals (select all vertices and Ctrl+N). Before you do this remove any double vertices or intrnal faces in your mesh. You can switch on/off the display of the normals in the mesh settings in edit mode (blender 2.4x) or in the display properties (N) in edit mode (blender 2.5x)

yeah, facenormals or invisible textures. (missing textures or face set to invisible in edit mode)