Inside the Strata Design 3D CX folder on your hard drive there is a Resources folder. Inside it is a Textures folder.
Placing your new textures there will allow Strata to find and load them at startup so they show up in the Resources Palette. If you create a new folder inside the Textures folder, then place your textures in it, they will show up under a Tab with the same name as the folder.
For more information about managing texture resources, see Chapter 8 - Texture Basics in the User Guide.