From Cainan:

How To use TexMod for cartography and other fun things.

I have researched this personally, and there is no security risk in running texmod.
it only alters game textures IN MEMORY while running. it does not make physical changes
to the game.

You can download texmod here:
http://www.tombraiderhub.com/tr7/modding/texmod/download/texmod.zip

For a full tutorial on how to use it, you can go here:
http://wiki.guildwars.com/wiki/Guide_to_modifying_in-game_graphics

That is the Official Guild Wars Wiki page on using Texmod
(no its not supported, but its not discouraged either)

You can find various 'packages' for use with Texmod here:
http://wiki.guildwars.com/wiki/Guide_to_modifying_in-game_graphics/Player_made_modifications

(I recommend the 'Cartography made easy' mods myself.)

Below i will give the simple method.
1: download Texmod and the 'packagge' or 'mod' that you will be using.
You will need to create a place for them to live.
I stored mine under D:\Program Files\Guild Wars\TexMod\

2: Start Texmod
in the 'target application box, click the 'open folder' icon and choose browse,
Navigate to where you stored guildwars, and select gw.exe. click 'open'.

3: Be sure 'Package mode' is selected.
there will be 4 butons in the middle. a open folder (add), an 'X'(remove), and an up and down arrow.
chose the 'add' icon, and select the package file you wish to use (it will be a .tpf file)
do this for each package you wish to use.

4: hit 'run'
This will start guildwars with the mods activated.
These are texture mods that ONLY YOU WILL SEE.
If you run Guild Wars w/o using TexMod to launch it, you will no longer see the mods.

As always, if you have questions, feel free to ask.
Hell, i may even know the answer!
-- Cainan