The first thing to do, in order to simplify things, owuld be to copy your textures into the same directory as the .pof file. That way, any path shenanigans can be ruled out.
Secondly, make sure that the textures are in a format PCS2 can understand. JPEG, Targa, or preferably DDS are all supported. Third, make sure that the filenames in the texture list in PCS2 do NOT have any extensions (i.e. If the texture name shows up as "name.tga" or "name.dds" or something, remove the file type extension).