Textures in 3D need to be softimage .pic format. You can get a filter on this site or Soft site that will let Photoshop read/write this format directly. Otherwise create a .tga file and bring up Soft DOS prompt then type:
tga2soft oldfilename.tga newfilename.pic This will convert the file from .tga to .pic. You can convert .pic to .tga by using soft2tga command.
When applying the texture browse for the file. When you save the seen you will be prompted to that the file will be copied to your current database.
Hope this helps,
Urp