Launch the installer .exe file by right-clicking on it and choosing "Run as Administrator". THIS IS NOT OPTIONAL.

When the installer loads, make sure it has found the correct location of both your Fallout 3 and, Fallout New Vegas Installs. If not use the browse button to navigate to the correct game directories.

In the install location field, use the browse button to navigate to your preferred TTW installation directory. DO NOT INSTALL DIRECTLY TO YOUR FNV DIRECTORY.

To avoid known problems we highly recommend building your installation in short file path - C:\TTW\ - for example. A long file path like C:\Users\My Name\Documents\MyGames\TTW Build\ is NOT recommended.

Click Install.

Note: You will see a blank command prompt window pop up on occasion, this is normal and will happen several times as the patcher extracts all the needed files from your Fallout 3 directory and repacks the needed files into your Fallout New Vegas directory.

If you have Windows 8, you may have to press a key each time the command prompt comes up. Windows 7 and earlier versions do not have this problem.

The first time you run the patcher this will take some time, be patient and, let it run its course. It may appear as though the patcher freezes up from time to time, but please be patient.

The installer can take between 30 minutes to several hours depending on the speed of your computer. Primarily, it is based on your hard drive speed. For example, users with mirrored solid state drives, fast processors, and lots of ram will have sub 1-hour install times.
When the installer finishes it will ask if you would like it to make a FOMOD; TTW is much easier to install with a mod manager, though we don't recommend NMM. We suggest you allow it to make a FOMOD. If you would rather do a manual install (not recommended) see the instructions in the next section.

FOMM 0.13.21 can be used to install the FOMOD as well, but only if you have 64-bit Windows, swap out the FOMM .exe and have at least 8GB of RAM
FOMM 0.14.11.9 can handle the install without swapping out the FOMM.exe.
Mod Organizer works as well, though you'll have more trouble with HUD mods later, should you choose to use them.
Make sure your mod manager is closed. Navigate to the TTW install directory and move the FOMODs (TaleOfTwoWastelands_Main.fomod, TaleOfTwoWastelands_Options.fomod) to your NMM FNV mods folder (C:\Games\Nexus Mod Manager\Fallout New Vegas\Mods\ by default)

Open NMM and go to the "Mods" tab. Inside you should see two new FOMODs (Tale of Two Wastelands - Main files, Tale of Two Wastelands - Optional Files). Install Main Files first and the Optional Files afterward. If NMM shows the "Upgrade" dialog asking if you want to Upgrade or install normally, click No to install normally.
You're done! If this is your first time playing TTW, start a new game, otherwise load an existing save and enjoy A Tale of Two Wastelands. Additionally, you may want to download other TTW-compatible mods that are listed in the TTW Mod Releases Forum.