1. Unpack the chosen 7zip files to your main Fallout 3 Folder (the one with FalloutLauncher.exe in) the files will be placed into the correct folders inside the main data folder.
2. Unpack the Archive Invalidation Program.zip anywhere and run it. This stops the fallout 3 engine using the texture files in the packed BSA archives the game ships with and to use any additional supplied texture/data files added by the user.
3. Run game and enjoy the improved textures.
The 512x512 defaultsize textures will not increase the texture/processing load on video cards, obviously the 1024x1024 ones will.