The first thing it changes is gameplay speed. Running from one side of new reno to the other for the hundredth time gets a bit boring, so you can set up some keyboard keys to modify the speed to anywhere between 0.5x and 10x normal. It affects running speed and combat, but not the world map, sound, movies or talking heads.
The second thing is that there's no option to play fallout in a window, so I added a windowed mode. It messes up if you scroll the window around, but it makes alt-tabbing, working with two monitors and taking screenshots a lot easier.
Lastly, scrolling through the inventory gets a bit cumbersome if you have lots of stuff in it, so I tweaked it to let you use the mouse scroll wheel as well as the normal controls.
I've only tested it with the copy of fallout2.exe that comes with megamod 2, but it should work with a normal v1.02 US version too.
This one adds the option to make the middle mouse button do something useful, frame skipping in windowed mode and a way to force DirectInput into background mode.