Running on Windows 7 with 3GB RAM and an AMD Anthlon 64 X2 dual-core, 5.2GHz combined. Both games were bought over Steam, Fallout 3 GOTY and original New Vegas.
My issue is that when I run the installer, it somehow completely fails to find Fallout 3, even after I point it in the right direction. I'll start the installer and, well, let me quote the install log:
[collapse collapsed title="how can you not find it i told you where it is"][12/7/2014 7:34:03 PM] Looking for Fallout3.exe
[12/7/2014 7:34:03 PM] Fallout 3 not found, prompting user.
[12/7/2014 7:34:17 PM] User selected: C:\Program Files\Steam\steamapps\common\Fallout 3 goty
[12/7/2014 7:34:17 PM] Looking for FalloutNV.exe
[12/7/2014 7:34:17 PM] Found.
[12/7/2014 7:34:17 PM] Looking for Tale of Two Wastelands
[12/7/2014 7:34:17 PM] Default path found.
[12/7/2014 7:34:25 PM] Checking for required files...
[12/7/2014 7:34:25 PM] Fallout3.esm could not be found.
[12/7/2014 7:34:25 PM] Anchorage.esm could not be found.
[12/7/2014 7:34:25 PM] ThePitt.esm could not be found.
[12/7/2014 7:34:25 PM] BrokenSteel.esm could not be found.
[12/7/2014 7:34:25 PM] PointLookout.esm could not be found.
[12/7/2014 7:34:25 PM] Zeta.esm could not be found.
[12/7/2014 7:34:25 PM] Fallout - Meshes.bsa could not be found.
[12/7/2014 7:34:25 PM] Fallout - Misc.bsa could not be found.
[12/7/2014 7:34:25 PM] Fallout - Textures.bsa could not be found.
[12/7/2014 7:34:25 PM] Fallout - MenuVoices.bsa could not be found.
[12/7/2014 7:34:25 PM] Fallout - Sound.bsa could not be found.
[12/7/2014 7:34:25 PM] Fallout - Voices.bsa could not be found.
[12/7/2014 7:34:25 PM] Anchorage - Main.bsa could not be found.
[12/7/2014 7:34:25 PM] Anchorage - Sounds.bsa could not be found.
[12/7/2014 7:34:25 PM] ThePitt - Main.bsa could not be found.
[12/7/2014 7:34:25 PM] ThePitt - Sounds.bsa could not be found.
[12/7/2014 7:34:25 PM] BrokenSteel - Main.bsa could not be found.
[12/7/2014 7:34:25 PM] BrokenSteel - Sounds.bsa could not be found.
[12/7/2014 7:34:25 PM] PointLookout - Main.bsa could not be found.
[12/7/2014 7:34:25 PM] PointLookout - Sounds.bsa could not be found.
[12/7/2014 7:34:25 PM] Zeta - Main.bsa could not be found.
[12/7/2014 7:34:25 PM] Zeta - Sounds.bsa could not be found.
[12/7/2014 7:34:25 PM] Missing files detected. Aborting install.[/collapse]
All I can think that's causing the problem is that the installer thinks the files should be somewhere else - say, the folder just being named Fallout 3 and not Fallout 3 goty - except the installer worked just fine with the exact same files a week ago. Renaming it to just "Fallout 3" and double-checking that nothing was set to read-only did nothing.
The other possible cause I see is I uninstalled the non-GOTY version of the game sometime after that first attempt to install the mod, since it's a redundant use of hard drive space now, but that doesn't make sense either given that that's not where the installer was looking the first time anyway.