Note: Radiant isn't supported on Windows Vista or OSX (Because racism)
Today I'm going to show you to install all the mapping tools properly so you can start mapping for CoD4 Radiant is where maps are created on CoD, while it's not user-friendly, with experience, you can get some damn good results.
The requirements are, you must have some space on HDD (about 1-2gbs) and you must have CoD4 installed updated to at least version 1.4 (the updates are here and here)
Download for the tool is here (includes the 1.1 patch as well)
(If that doesn't work, go to here, here or here to download the mod tools and then download the small 1.1 update here.)
Once they're done downloading, open up 'cod4mw_modtools_v1.zip' and extract all the contents into you CoD4 root folder which is 'C:\Program Files (x86)\Activision\Call of Duty 4 - Modern Warfare' by default. Overwrite if it asks you, it may take a long time since you're extracting 600mb.
When that has finished, open up 'cod4mw_modtools_v1.1_update' and put the 'bin' folder in your root folder and overwrite the two files.
Now, go to your root folder and then the bin folder. In here are all the .exes for the tools you'll be using. However, in you go into the'Cod4CompileTools' folder, there's a file called 'Cod4CompileTools.exe' which has the compiling tools so you can compile your map and shortcuts to the other tools. You should get used to using this .exe because it's quite helpful.
When opened, the compile tools show you all the maps you've made and the buttons that compile your map but if we want to get to radiant or something else, click applications.
When you click applications, you'll see all the shortcuts to the main tools.
Then, when you press 'launch level editor', radiant will popup with unamed.map.
Go to file at the top and click 'set startup project'.
Then navigate to the bin folder in your CoD4 directory and select cod4.prj
Now your radiant is set up properly. You're ready to make maps on it, if you want to learn how to make a map, there are plenty tutorials out there that teach you!