TJMod setup - Client
To get TJMod running for you as a player, simply connect to either of the official servers and make sure you've got cl_allowdownload 1 set.
To do it manually, firstly download the latest version of TJMod, which you can find at the top of the TJMod forum section.
Then unzip this in your ET directory, so you'd have e.g.
C:/Program Files/Wolfenstein - Enemy Territory/tjmod/
A somewhat common error is Client/Server game mismatch
This is usually caused by having multiple tjmod_x-x-x.pk3 files in your tjmod directory. A safe fix for this is to delete your current tjmod directory, and then re-download the newest version of tjmod and unzipping it in the ET directory.
Though in most cases it's enough to just go into the directory and delete any .pk3 files which isn't for the newest tjmod version.
Note: It could be a smart choice to backup your configs and profiles folder (tjmod/profiles) before deleting anything.
If you're still encountering this problem, post it in the forum!
TJMod setup - Server
To get TJMod running on a server, simply download the newest version and unzip the tjmod folder to your desktop. Then upload this folder to your server's ET directory.
Then start the server with +set fs_game tjmod
If you want a custom config, take a look at the Cvar list (scroll down for serverside).
This example config might also be handy: Server config example (Official 2.60b)
If you're having problems with either server or client setup, feel free to post in the forums.
(Or maybe ask setup, I've got a that feeling he _should_ know this!)