NWNExplorer Reborn can help you find resources, but, and this is a big BUTT, NWN resources are not necessarily ordered as you might expect.
The game works by patch level. When you open the resource list in NWNExplorer, you see, NWN, NWNpatch-bahblah etc... NWNSOU, NWNSOUPatch-BlahBlah, NWNHotUPatch-BlahBlah, then 1.69 patch etc. EACH of those has sub-folders, each of those sub-folders may or may not have additional sub-folders. Regardless though, NWN the game, takes the resources in reverse order. Path 1.69 overrides 1.67 which overrides Hotu, which Overrides SoU, which overrides the Main NWN.
So, you have to start your searches backwards, and can easily get lost attempting to find stuff.
Now, the Game engine searches in this order, .HAK from your hak folder, THEN nwn\\override THEN the various main game resources located in the various .BIF files think of them as .HAK files with higher priority. Taking all of that into account, vid/texture resources are handled following that order, but also use an extra control bit. If a GAME resource (patch file, SoU, HotU, Main NWN) file has the same name as a file located in override or hak, AND if that resource is a DDS (texture) type of resource then the Game version takes control over any .TGA of same filename. IE: DDS overrides .TGA regardless of location. Now, if you have a .DDS in ANY .HAK attached to the mod, then the version in your .HAK will override the main game resource, but if all you have in your .HAK is a .TGA, then the main game resource takes control. I am not sure where .PLT falls in the texture resource lists so I can't answer that possible question.
I run into the same sort of problem inside of 3ds, since 3ds does NOT recognize BIoware .DDS files, I must have a .TGA to work with when developing. I just remember to remove the .TGA unless mine is actually different than the game version. If it IS different, I make sure to rename it in the .MDL and actual filename, so that it does NOT attempt to override any real game resource file.
Plain as butter? <warning, slippery sloped question there>