I have 8 Gigs of RAM on a Windows 8 machine and I still experience the crash on vanilla Fallout New Vegas.
The crash is complicated and very hard to explain and a wide array of things can cause it, but I will do my best to explain it.
First type of crash that I experience and happens most often is the traveling/loading crash. This crash occurs when I'm going through two areas of the level with an upgraded/scripted weapon. What will happen is the game deconstructs old weapons, including yours, and then reconstructs them in the new cell. By doing this, it has to know by the code which one to take, and sometimes it leaves shit out that the weapon draw function grabs when it's called normally. To fix it, just fast travel and go through doors with your fists out.
The second type of crash I experienced with a null pointer to hair mesh that was found on bald people like Chris from the rocket experiment. This can be fixed by using Mission Mojave but seeing as TTW doesn't meld well with it, I wouldn't use it. They may have fixed this already they may not have.
The third type of crash I experienced was codec/driver inter-cooperation problems. Mainly codecs. If you have like K-Lite codec pack or the CCCP, uninstall it. It just pisses off Fallout because of Bink. Another problem was with the driver interface between the engine and the driver was getting hooked by Steam. The game was designed on the eggsbawx three sistein(proven of Tod's E3 gameplay), so it wasn't designed to have the steam overlay. They just kinda threw that on for the PC port last minute, which is very obvious with the half-assed steam interface the game uses. Basically anything that gets in the way of runtime and the computer fucks with Fallout. Try to run your computer as vanilla as possible.
The fourth type of crash I experienced was just flat out fucking memory starvation. There just isn't enough room in the RAM to store this much information. You're going from Fallout New Vegas, which already has a shit-load of information, to both Fallout 3 and New Vegas in one runtime, the game has to store everything you do to RAM. If you move a bottle, its new location and its structure has to be put to RAM. Opening chests, storing shit in chests, shooting someone basically the more you play the more you fill up the RAM. I have 8GB and the 4GB fix did not help me at all.
I hope this helps explain it. I know it's really annoying to keep restarting the game, and usually when it crashes I just stop playing because it breaks immersion, but try to power through it.
EDIT: ALT+TABing is also known to cause it, but that should go without saying.
This is seeming less and less like a patch solution and more like a warez distro fix.