Mmm Craig. It may be in
PSP, but just different buzz words.
In
PS you have to save out a native PSD file first. Perhaps you have to save a native
PSP file of the background?
The actual texture mapping is done in the Texture filter of
PS. There is a pop-up in that dialog box that let's you load graphics or textures saved as PSD. JPEG doesn't work, nor TIFF.
Seems that if you can load 3rd party textures, you could load a
PS file as a texture map.
Sorry, if you can't do that, but then you have access to cool Windows stuff that I can't do. :-)