Convert Textures to the Petz Palette using IrfanView

First, get IrfanView here.
Then, download the PetzPalette for IrfanView

Load up your texture.
Then go to Image -> Palette -> Import Palette.
Locate and select the Petz Palette.

Your texture will probably change colours a little bit.
Now save as a .bmp and you should be ready to go!