step one: Open your texture [it should be 256x256] if its not 256x256 just re-size it. also open the snap shot you took in your map [if you didnt do this go into your map and press ctrl-p]

step two: Select your bmp file so that the title bar is blue and the pcx 
title bar is grey. then, go up to edit in the menu bar and select copy.
then select your snapshot [pcx file] and select paste and paste it as new selection. then after that go to edit and select copy again then paste as new image. A new window should pop up, this is the pcx you will convert to a map file so save this image as mytexture.bmp. you can trash the old one I dont really care. where mytexture is the name of your texture. I recommend to put a number for each size of your texture so that you'll know which is which. THE POINT OF DOING THIS IS TO MAKE YOUR TEXTURES PALLET THE SAME AS THE GAMES!!! so it wont look trashed.  repeat this process with all the other sizes [128x128, 64x64, 32x32]

step three: this is tricky so read carefully.
now before you start editing the trn file this part you need to make your bmp files in to map files. to do this move all the bmp files you made into the folder where bmp2map is installed. then in windows explorer go to that directory and drag your file to the bmp2map file and it should open a window saying that it has been converted. [note that you need dos4gw installed into your windows/system folder to make bmp2map work, get this file at www.geocities.com/SiliconValley/Campus/9664/]
after you have converted all your files put all your new map files into the addon folder of battlezone.

now youre ready to edit the trn file.open the trn file that has your map name, example multdm07.trn, you should see a bunch of text. go down to where it says texturetype0. look below for example.

[TextureType0] // Lava
FlatColor= 134
SolidA0        = io00sA0.map
SolidA1        = io00sA1.map
SolidA2        = io00sA2.map
SolidA3        = io00sA3.map
SolidB0        = io00sA0.map
SolidB1        = io00sA1.map
SolidB2        = io00sA2.map
SolidB3        = io00sA3.map
SolidC0        = io00sB0.map
SolidC1        = io00sB1.map
SolidC2        = io00sB2.map
SolidC3        = io00sB3.map
SolidD0        = io00sC0.map
SolidD1        = io00sC1.map
SolidD2        = io00sC2.map
SolidD3        = io00sC3.map

now delete all the places where it says solidA0 etc it should look like this

[TextureType0] // Lava
FlatColor= 134

now, replace it with this

[TextureType0] // Lava
FlatColor= 134
SolidA0        = mytexture1.map
SolidA1        = mytexture2.map
SolidA2        = mytexture3.map
SolidA3        = mytexture4.map

now you can use your texture in your map!!!
if you more textures just go to texturetype1 and do the same thing [you can only have 7 texturetypes I think] 

and thats it, I hope you understood these instructions cause I dont think it gets any clearer than this.