I had black out problems also and found that I had internet explorer running before starting Fallout. If I shut down internet explorer the black out problem no longer is an issue.
When I first installed Fallout I got rid of the ddraw.dll file for better performance and then installed the High-Res 1.3 mod without a problem. The game played great for a little bit until it started blacking out constantly. At first it wasn't too much of a problem as I could just keep moving my mouse to the edge of the screen to remove the black. But now it is becoming a real nuisance. Every 2 - 5 seconds my screen will black out and I have to move my mouse erratically like a toddler on guarana. I read around the GOG.com forums and followed a lot of advice including:
Installing Timeslip's engine fix.
Renaming either the new ddraw.dll file or falloutw.exe
Changing the settings of Timeslip's ddraw.dll
or even downright uninstalling the High-Res mod.
Unfortunately none of these worked. I don't know what to do and it is really, really annoying. The game is playable but not enjoyable if every few seconds I get interrupted by a blackout. Any help, advice, instructions I didn't follow, et cetera? Much appreciated. ^^
Edit: I realized what was causing the blackouts and it's simply renaming or removing the original ddraw.dll. If I were to replace it with anything else I would constantly blackout. Is there some way around this? The original ddraw.dll file makes the the game terribly slow and I can't play with it or without it... ='(
Edit 2: While nothing works for me I realized that simply letting the program run for an hour or so lessens the amount of black-outs to nearly zero. Also, starting a game from scratch produces nearly no blackouts until you exit and load a saved game. Then the blackouts become unbearable until you let the application run for a while. Really, really weird... O.o
Edit 3: And now the blackouts are completely gone. What a fickle game... Oh well, time to enjoy.