Begin the installation of GtkRadiant by clicking on the file you downloaded. You will then be asked a number of questions. The following are good answers :]

1. Install GtkRadiant Core Files into d:\GtkRadiant\
2. You are then asked for the install path for the Quake 3 Game mod. Select d:\quake3\ (If you have Quake 3 install, select your installation path instead)
3. You will now be prompted for a folder name for these file. The default is Radiant and there is no reason to change this, press the next button
4. Next question is about Return to Castle Wolfenstein. Unless you have RtCW installed leave the defaults. We will not be installing RtCW but you can not skip this question. (If you do have RtCW, select the correct folder)
5. Again you are prompted for the installation folder, this time for RtCW. As we will not be installing these file, press next. (Even if you do want to install RtCW files later, press next)
6. Set-up type allows us to configure which files to install. Make sure you select 'Custom' install
7. The components you want to select are the GtkRadiant Core, Manual, Plugins, Misc Manuals. Under the Quake 3 option, select the Quake III Editing media. Everything else is optional. See this screenshot.
8. Next is the Program Folder option, hit next or change to suit your personal desires. You are then shown a screen that will display what is about to be copied to your hard drive, I have no idea why all this detail is really needed, but anyway.
9. Even through we selected to not install any RtCW files you may note that a RtCW folder has been created in C:\Program Files\. Just delete it. You have no need for it. (Well, ok, you may have a need for it you want to edit for RtCW as well. Its your choice)
10. GtkRadiant is now installed BUT it is not configured yet. Do not start it up yet!

NOTE: Do NOT start GtkRadiant yet. You may cause too many problems. Wait until we have everything configured.