There is a tool called FO3 RAM Boost that I used to make my fallout 3 game run better since Fallout 3 is a 32-bit program, it does not use more than 2GB RAM on either 32-bit or 64-bit systems. This utility helps to make Fallout 3 handle more than 2GB address space on any system with more than 2GB of RAM. (But I am using it for NEW VEGAS) since i am I have 2.6 gigs of ram on my system.

Your not changing the Memory Map of the program, just it's ability use memory that is addresses above 2GB.

If it helps, great, but it won't make the game run better because it makes the game do something it can't do, which is use more than it's designed memory map.

Contrary to popular belief, that tool is meaningless to the vanilla game. FO:NV and FO3's memory footprint hovers around 1GB at max no matter what. All it takes is a trip to the task manager to verify this

Apparently mods that load high resolution textures made by the community will override this 1GB limit and in that case it is claimed that it helps. Regardless, anybody that says "I got a huge fps boost" is just observing the placebo effect. In theory, if the game began to occasionally stutter while streaming new assets in and out of virtual/physical ram (due to low memory) then maybe it wouldn't stutter at that point but it isn't going to have any effect on average FPS.

If your system only has 2.6GB of RAM, making the game large address aware won't help out at all. Windows is already reserving a large portion of that 2.6gb for itself and the swap file would come into effect anyways which would zero out any performance increase (again, in theory if one existed but it doesn't - 1GB footprint only)