I tried to follow superJer's instructions and had a hard time fiquring it out how to make my ladder. All I got was confused. I finally got my ladder. Here is how:
First thing you do when you create a ladder, is to make the main shape of your ladder. I used the "{CSTRIKE_LE6LAD" texture from the cstrike.wad.
NOTE: textures with "{" infront of them can/will become transparent through the blue in the texture, if you make it an entity, and select the correct options.
Ignore the blue in the texture, this will become transparent, so that you can look see it.
Then I made the texture see-through, by selecting the ladder brush, and making it an entity, by pressing Crtl-T. Now, choose func_wall in the drop-down menu, and set these options in it:
Render mode: Solid
FX Amount: 255
Now you will be able you see through the ladder, but if you compile your map, you won't be able to climb the ladder.
So next:
Create an other brush, which has the exact same size, as your original ladder brush. Use the "AAAtrigger" texture on it.(I got this from the zhlt.wad.)
Now make this brush, a ladder entity, by Crtl-T, and picking func_ladder. Now you have to place the new brush infront of the func_wall, and you got your ladder.
Hope this helps
I am not sure what the clip texture does but maybe you can tell me
I am always watching. You just may not see me!