If you own Skyrim (Oldrim) you can download the CKIT for it on steam and copy some additional resources from the installation to complete your GECK install for both Fallout 3 and Fallout: New Vegas.WARNING Do not 4GB patch the Fallout 3 GECK, it will cause it to crash more frequently.You can download and install the GECK Extender and its patcher from here If you are using the Fallout 3 GECK, you will probably want it to load FOSE automatically as well as fix bugs and add some features to GECK that were removed by the developers.Alternatively, you can use the NTCore 4GB patch available here, but this is unsupported. You can download and install the GECK Extender and its patcher from here. If you are using the Fallout: New Vegas GECK, you will probably want to make it large address aware and have it load NVSE automatically as well as fix bugs and add some features to GECK that were removed by the developers.
You cannot use it to mod the X-Box 360 or PS3 console versions of the game. See the note below under Loading and Testing Your Plugin for more information. If you have already installed them into one of these folders, either uninstall them and reinstall them into a location like C:\Games or C:\Fallout, or, when using the Geck, do not run it as administrator. These folders are protected by the operating system and require you to take additional steps when creating and using mods.