In BI both sides of a face should be textured by default in the render.
If you mean in the viewport, you can switch the viewport shading to Textured in 3D view > Header and set the shading to GLSL in 3D view > Properties region (N) > Shading. Also make sure that Backface Culling is disabled in the same panel.
Note that you will need to add lamps to the scene, or enable temporarily Shadeless in Properties > Material > Shading.
Shadeless is good for editing purposes where you want to see the texture everywhere (no shadows or shading). Note that this will affect the final render, so remember to disable it when you are done.
For unhiding faces, press AltH, or 3D view > Header > Mesh > Show/Hide > Show hidden in edit mode.