The www_wulfen_texture_pack_20_fix.pk4 file enables to use all the Wulfen and Monoxead textures to work without require the SikkMod !!! So you can and should, simply copy the file www_wulfen_texture_pack_20_fix.pk4 to your "Doom 3/base" directory and of course you need to copy the Wulfen and Monoxead .pk4 files into the "Doom 3/base" directory too, so you can use and be amazed with the new highres textures for your Doom 3 game.
Also, you can copy the file www_High-Res_Pipes_unofficial_wulfen_20_update.pk4 to the "Doom3/base" directory, that enables highres pipes, but for this pipes file to work, remember that the original file, even it is named as www_High-Res_Pipes_unofficial_wulfen_20_update.pk4 in reality it is a .rar file so, you would require first to convert it to a .zip file, with the WinRAR program available on the net. After done with this, you should rename the resulting www_High-Res_Pipes_unofficial_wulfen_20_update.pk4.zip file into www_High-Res_Pipes_unofficial_wulfen_20_update.pk4, so it ends in .pk4 and it can work with Doom 3.
So, you need at least this files to be copied to your "Doom 3/base" directory...: